This is a compilation of acronyms commonly used in astronomy. Most of the acronyms are drawn from professional astronomy and are used quite frequently in scientific publications. However, a few of these acronyms are frequently used by the general public or by amateur astronomers

Amateur astronomy

Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...

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The acronyms listed below were placed into one or more of these categories:

• Astrophysics terminology – a general category for physics-related acronyms
• Catalog
  Astronomical catalog
  An astronomical catalog or catalogue is a list or tabulation of astronomical objects, typically grouped together because they share a common type, morphology, origin, means of detection, or method of discovery...
  
   – a category for collections of tabulated scientific data
• Communications network – a category that includes any network that functions primarily to communicate with spacecraft
  Spacecraft
  A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
  
   rather than performing astronomy
• Data – a general category for astrophysical data not associated with any single catalog or observing program
• Celestial object
  Astronomical object
  Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...
  
   – a category that contains acronyms for natural objects in space and for adjectives applied to objects in space
• Instrumentation
  Instrumentation
  Instrumentation is defined as the art and science of measurement and control of process variables within a production, or manufacturing area....
  
   – a category for telescope and other spacecraft equipment, particularly detectors such as imagers and spectrometer
  Spectrometer
  A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
  
  s
• Meeting – a category for acronyms used to describe meetings that are not named after organizations
• Observing program – an astronomical program, often a survey, performed by one or more individuals; may also refer to the group that performs the survey
• Organization – a category for any large private organization, government organization, or company
• Person – a category form terms that refer to individual people
• Publication – a category for acronyms used for magazines, scientific journals, and similar astronomy-related publications
• Software – a category for all software except catalogued data (which is listed under "catalog") and scientific images
• Spacecraft
  Spacecraft
  A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
  
   – a category that includes all spacecraft except space telescopes
• Telescope
  Telescope
  A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
  
   – a category that includes both ground-based and space telescopes; organizations that operate telescopes (for example, the National Optical Astronomy Observatory (NOAO)
  National Optical Astronomy Observatory
  The National Optical Astronomy Observatory is the United States national observatory for ground based nighttime ultraviolet-optical-infrared astronomy. The National Science Foundation funds NOAO to provide forefront astronomical research facilities for US astronomers...
  
  ) are listed under "organization"

0–9

• 1RXH – (catalog) 1st ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   X-ray HRI, a catalog of sources detected by ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   in pointed observations with its High Resolution Imager
• 1RXS – (catalog) 1ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   X-ray Survey, a catalog of sources detected by ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   in an all-sky survey
• 2dF – (instrumentation) Two-degree Field, spectrograph on the Anglo-Australian Telescope
  Anglo-Australian Telescope
  The Anglo-Australian Telescope is a 3.9 m equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia at an altitude of a little over 1100 m...
  
  
• 2dFGRS
  2dF Galaxy Redshift Survey
  In astronomy, the 2dF Galaxy Redshift Survey , 2dF or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory with the 3.9m Anglo-Australian Telescope between 1997 and 11 April 2002. The data from this survey were made public on 30 June 2003...
  
   – (observing program) Two-degree-Field Galaxy Redshift Survey
• 2MASP – (catalog) Two-Micron All Sky Survey Prototype, an early version of the 2MASS catalog
• 2MASS – (observing program/catalog) Two-Micron All Sky Survey, an all-sky survey in the near-infrared; also used to describe the catalog of sources from the survey
• 2MASSI – (catalog) Two-Micron All Sky Survey, Incremental release, one of the versions of the 2MASS catalog
• 2MASSW – (catalog) Two-Micron All Sky Survey, Working database, one of the versions of the 2MASS catalog
• 2SLAQ – (observing program) 2dF-SDSS
  Sloan Digital Sky Survey
  The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P...
  
   LRG And QSO
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
   survey
• 6dF – (instrumentation) Six-degree Field, spectrograph on the UKST
  UK Schmidt Telescope
  The 1.2 metre UK Schmidt Telescope is operated by the Australian Astronomical Observatory , and located adjacent to the 3.9 metre Anglo-Australian Telescope at Siding Spring Observatory, Australia...
  
  

A

• A&A – (publication) Astronomy & Astrophysics, a European scientific journal
• AAA – (organization) Amateur Astronomers Association of New York
• AAO – (organization) Australian Astronomical Observatory (prior to 1 July 2010: Anglo-Australian Observatory)
• AAS
  American Astronomical Society
  The American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC...
  
   – (organization) American Astronomical Society
• AAT
  Anglo-Australian Telescope
  The Anglo-Australian Telescope is a 3.9 m equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia at an altitude of a little over 1100 m...
  
   – (telescope) Anglo-Australian Telescope
• AAVSO
  American Association of Variable Star Observers
  Since its founding in 1911, the American Association of Variable Star Observers has coordinated, collected, evaluated, analyzed, published, and archived variable star observations made largely by amateur astronomers and makes the records available to professional astronomers, researchers, and...
  
   – (organization) American Association of Variable Star Observers
• ABBA – ADC Backend For Bolometer Array
• ABRIXAS
  A Broadband Imaging X-ray All-sky Survey
  A Broadband Imaging X-ray All-sky Survey, or ABRIXAS was a space-based German X-ray telescope. It was launched on 28 April 1999 in a Cosmos launch vehicle from Kapustin Yar, Russia, into Earth orbit...
  
   – (observing program) A BRoadband Imaging X-ray All-sky Survey
• AC – (catalog) Catalogue Astrographique
• ACE
  Advanced Composition Explorer
  Advanced Composition Explorer is a NASA space exploration mission being conducted as part of the Explorer program to study matter in situ, comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE is used by the Space Weather...
  
   – (spacecraft) Advanced Composition Explorer
• ACIS
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
   – (instrumentation) Advanced CCD Imaging Spectrometer, an instrument on the Chandra X-Ray Observatory
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
  
• ACM – (meeting) Asteroids, Comets, and Meteors
• ACP – (instrumentation) – Aerosol Collector and Pyrolyser, an instrument on the Huygens probe
  Huygens probe
  The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
  
  
• ACS
  Advanced Camera for Surveys
  The Advanced Camera for Surveys is a third generation axial instrument aboard the Hubble Space Telescope . The initial design and scientific capabilities of ACS were defined by a team based at Johns Hopkins University. ACS was assembled and tested extensively at Ball Aerospace & Technologies Corp...
  
   – (instrumentation) Advanced Camera for Surveys, an instrument on the Hubble Space Telescope
• ACV
  Alpha2 Canum Venaticorum variable
  An Alpha2 Canum Venaticorum variable is a type of variable star. These stars are chemically peculiar main sequence stars of spectral class B8p to A7p. They have strong magnetic fields and strong silicon, strontium, or chromium spectral lines...
  
   – (celestial object) Alpha Canes Venatici, a class of rotating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s with strong magnetic field
  Magnetic field
  A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
  
  s named after Alpha Canum Venaticorum (Cor Caroli)
  Cor Caroli
  Cor Caroli is the brightest star in the northern constellation Canes Venatici...
  
  , the archetype for the class
• ACYG
  Alpha Cygni variable
  Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time others parts expand. They are supergiant stars of spectral types B or A...
  
   – (celestial object) Alpha CYGni, a class of rotating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after Alpha Cygni (Deneb)
  Deneb
  Deneb is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars...
  
  , the archetype for the class
• ADAF – (astrophysics terminology) Advection Dominated Accretion Flow, a mechanism by which matter is slowly accreted onto a black hole
  Black hole
  A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
  
  
• ADC – (organization) Astronomical Data Center
• ADEC – (organization) Astrophysics Data Centers Executive Council, an organization that provides oversight for the Astrophysics Data and Information Services
• ADF – (organization) Astrophysics Data Facility
• ADS – (catalog) Aitken Double Stars
• ADIS – (organization) Astrophysics Data and Information Services
• ADS
  Astrophysics Data System
  The Astrophysics Data System , developed by the National Aeronautics and Space Administration , is an online database of over eight million astronomy and physics papers from both peer reviewed and non-peer reviewed sources...
  
   – (organization) Astrophysics Data Service, an organization that maintains an online database of scientific articles
• AFGL – (organization) Air Force Geophysics Laboratory, a research laboratory now part of the United States Air Force Research Laboratory
  Air Force Research Laboratory
  The Air Force Research Laboratory is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of affordable aerospace warfighting technologies; planning and executing the Air Force science and...
  
  
• AFOEV – (organization) Association française des observateurs d'étoiles variables
• AG
  Astronomische Gesellschaft
  The Astronomische Gesellschaft is an astronomical society established in 1863 in Heidelberg, the second oldest astronomical society after the Royal Astronomical Society....
  
   – (organization) Astronomische Gesellschaft
• AGAPE – (observing program) Andromeda Galaxy and Amplified Pixels Experiment, a search for microlens
  Microlens
  A microlens is a small lens, generally with a diameter less than a millimetre and often as small as 10 micrometres . The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects arise due to optical diffraction at the small features...
  
  es in front of the Andromeda Galaxy
  Andromeda Galaxy
  The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
  
  
• AGB
  Asymptotic Giant Branch
  The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass stars. This is a period of stellar evolution undertaken by all low to intermediate mass stars late in their lives....
  
   – (celestial object) Asymptotic Giant Branch, a description for a type of red giant star
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
  
• AGK – (catalog) Astronomische Gesellschaft Katalog
• AGN
  Active galactic nucleus
  An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
  
   – (celestial object) Active Galactic Nucleus
• AGU
  American Geophysical Union
  The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
  
   – (organization) American Geophysical Union
• AIM
  Aeronomy of Ice in the Mesosphere
  The Aeronomy of Ice in the Mesosphere is a satellite to conduct a 26-month study of noctilucent clouds . It is the ninetieth Explorer program mission and is part of the NASA-funded Small Explorer program...
  
   – (spacecraft) Aeronomy of Ice in the Mesosphere, a spacecraft that will study the Noctilucent cloud
  Noctilucent cloud
  Night clouds or Noctilucent clouds are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night...
  
  s
• AIPS
  Astronomical Image Processing System
  The Astronomical Image Processing System is a package to support the reduction and analysis of data taken with radio telescopes. It is most useful for arrays of telescopes like the VLA and VLBA and the WSRT...
  
   – (software) Astronomical Image Processing System
• AJ
  Astronomical Journal
  The Astronomical Journal is a peer-reviewed monthly scientific journal owned by the American Astronomical Society and currently published by Institute of Physics Publishing. It is one of the premier journals for astronomy in the world...
  
   – (publication) Astronomical Journal
• ALaMO
  Alamo
  The Battle of the Alamo was a battle fought during the Texas Revolution.Alamo may also refer to:-Places:*Alamo Mission in San Antonio, Texas*Alamo, California*Alamo, Georgia*Alamo Township, Michigan*Alamo, Nevada*Alamo, New Mexico...
  
   – (organization) Automated Lunar and Meteor Observatory
• ALEXIS
  Array of Low Energy X-ray Imaging Sensors
  The Array of Low Energy X-ray Imaging Sensors X-ray telescopes feature curved mirrors whose multilayer coatings reflect and focus low-energy X-rays or extreme ultraviolet light the way optical telescopes focus visible light...
  
   – (instrumentation) Array of Low Energy X-ray Imaging Sensors
• ALMA
  Atacama Large Millimeter Array
  The Atacama Large Millimeter/sub-millimeter Array is an array of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array is being constructed on the Chajnantor plateau at 5000 metres altitude...
  
   – (telescope) Atacama Large Millimeter/Sub-millimeter Array
• ALPO
  Association of Lunar and Planetary Observers
  The Association of Lunar and Planetary Observers is an international scientific and educational organization established in March, 1947 in the United States by Walter H. Haas, and later incorporated in 1990...
  
   – (organization) Association of Lunar and Planetary Observers
• AMANDA
  Antarctic Muon And Neutrino Detector Array
  The Antarctic Muon And Neutrino Detector Array is a neutrino telescope located beneath the Amundsen-Scott South Pole Station. In 2005, after nine years of operation, AMANDA officially became part of its successor project, the IceCube Neutrino Observatory.AMANDA consists of optical modules, each...
  
   – (telescope) Antarctic Muon And Neutrino Detector Array, a neutrino telescope
• AMASE – (software) Astrophysics Multi-spectral Archive Search Engine
• AMS
  American Meteor Society
  The American Meteor Society, Ltd. is a non-profit scientific organization established to encourage and support the research activities of both amateur and professional astronomers who are interested in the field of Meteor Astronomy...
  
   – (organization) American Meteor Society
• AN
  Astronomische Nachrichten
  Astronomische Nachrichten , one of the first international journals in the field of astronomy, was founded in 1821 by the German astronomer Heinrich Christian Schumacher. It claims to be the oldest astronomical journal in the world that is still being published...
  
   – (publication) Astronomische Nachrichten, a German scientific journal
• ANS
  Astronomical Netherlands Satellite
  The Astronomical Netherlands Satellite was a space-based X-ray and ultraviolet telescope. It was launched into Earth orbit on 30 August 1974 at 14:07:39 UTC in a Scout rocket from Vandenberg Air Force Base, United States...
  
   – (telescope) Astronomical Netherlands Satellite
• ANS – (organization) Astro News Service
• ANSI
  American National Standards Institute
  The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...
  
   – (organization) American National Standards Institute
• AO
  Adaptive optics
  Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
  
   – (instrumentation) Adaptive Optics
• AOR – (instrumentation) Astronomical Observation Request
• ApJ
  Astrophysical Journal
  The Astrophysical Journal is a peer-reviewed scientific journal covering astronomy and astrophysics. It was founded in 1895 by the American astronomers George Ellery Hale and James Edward Keeler. It publishes three 500-page issues per month....
  
   – (publication) Astrophysical Journal
  • ApJL – (publication) Astrophysical Journal Letters
  • ApJS – (publication) Astrophysical Journal Supplement Series
• APM – (instrumentation/catalog), Automatic Plate Measuring machine, describes both a machine for making measurements from photographic plates and a catalog based on measurements by the machine
• APO
  Apache Point Observatory
  The Apache Point Observatory is located in the Sacramento Mountains in Sunspot, New Mexico 18 miles south of Cloudcroft. The observatory consists of the Astrophysical Research Consortium's 3.5-meter telescope, the Sloan Digital Sky Survey 2.5-m telescope with a 20" photometric telescope,...
  
   – (organization) Apache Point Observatory
• APOD
  Astronomy Picture of the Day
  Astronomy Picture of the Day is a website provided by NASA and Michigan Technological University . According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer."The photograph is not necessarily...
  
   – (data) Astronomy Picture of the Day
• APT
  Automated Patrol Telescope
  The Automated Patrol Telescope is a wide-field CCD imaging telescope, which is operated by the University of New South Wales at Siding Spring Observatory, Australia.-External links:* on the internet...
  
   – (telescope) Automated Patrol Telescope
• ARC – (organization) Ames Research Center
• ARC – (organization) Astrophysical Research Consortium
• ASA – (organization) Astronomical Society of the Atlantic
• ASI – (organization) Agenzia Spaziale Italiana
• ASIAA – (organization) Academia Sinica Institute of Astronomy and Astrophysics
• ASP
  Astronomical Society of the Pacific
  The Astronomical Society of the Pacific is a scientific and educational organization, founded in San Francisco on February 7, 1889. Its name derives from its origins on the Pacific Coast, but today it has members all over the country and the world...
  
   – (organization) Astronomical Society of the Pacific
• ASTRO
  Orbital Express
  thumb|Orbital Express: ASTRO and NEXTSatOrbital Express was a space mission managed by the United States Defense Advanced Research Projects Agency and a team led by engineers at NASA's Marshall Space Flight Center...
  
   – (spacecraft) Autonomous Space Transport Robotic Operations
• ATA
  Allen Telescope Array
  The Allen Telescope Array , formerly known as the One Hectare Telescope , was a joint effort by the SETI Institute and the Radio Astronomy Laboratory at the University of California, Berkeley to construct a radio interferometer that is dedicated to astronomical observations and a simultaneous...
  
   – (telescope) Allen Telescope Array, a radio interferometer array
  Astronomical interferometer
  An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....
  
   developed by the SETI Institute
  SETI Institute
  The SETI Institute is a not-for-profit organization whose mission is to “explore, understand and explain the origin, nature and prevalence of life in the universe”. SETI stands for the "search for extraterrestrial intelligence". One program is the use of both radio and optical telescopes to search...
  
   to search for possible signals from extraterrestrial life
• ATCA
  Australia Telescope Compact Array
  The Australia Telescope Compact Array is a radio telescope at the Paul Wild Observatory, twenty five kilometres west of the town of Narrabri in Australia....
  
   – (telescope) Australia Telescope Compact Array
• ATM
  Amateur telescope making
  Amateur telescope making is the activity of building telescopes as a hobby, as opposed to being a paid professional. Amateur telescope makers build their instruments for personal enjoyment of a technical challenge, as a way to obtain an inexpensive or personally customized telescope, or as a...
  
   – (person) hobbyist engaged in Amateur telescope making
  Amateur telescope making
  Amateur telescope making is the activity of building telescopes as a hobby, as opposed to being a paid professional. Amateur telescope makers build their instruments for personal enjoyment of a technical challenge, as a way to obtain an inexpensive or personally customized telescope, or as a...
  
  (may also refer to the book of the same title, Amateur Telescope Making
  Amateur Telescope Making
  Amateur Telescope Making is a series of three books edited by Albert G. Ingalls between 1926 and 1953 while he was an associate editor at Scientific American. The books cover various aspects of telescope construction and observational technique, sometimes at quite an advanced level, but always in...
  
  )
• AU
  Astronomical unit
  An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
  
   – (measurement) Astronomical Unit, the distance between the Earth and the Sun
• AUASS – (organization) Arab Union for Astronomy and Space Sciences
• AURA
  Association of Universities for Research in Astronomy
  The Association of Universities for Research in Astronomy is a consortium of universities and other institutions that operates astronomical observatories and telescopes...
  
   – (organization) Association of Universities for Research in Astronomy
• AWCA – (meeting) American Workshop on Cometary Astronomy, an older name for the International Workshop on Cometary Astronomy
• AXP
  Anomalous X-ray pulsar
  Anomalous X-ray Pulsars are now widely believed to be magnetars—young, isolated, highly magnetized neutron stars. These energetic X-ray pulsars are characterized by slow rotation periods of ~2–12 seconds and large magnetic fields of ~1013–1015 gauss . There are currently 9 known and 1 candidate...
  
   – (celestial object) Anomalous X-Ray Pulsar
• AXAF
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
   – (telescope) Advanced X-ray Astrophysics Facility, an older name for the Chandra X-ray Observatory
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
  

B

• B – (catalog) Barnard catalog
• BAA – (organization) British Astronomical Association
• BAAS
  Bulletin of the American Astronomical Society
  Bulletin of the American Astronomical Society is the journal of record for the American Astronomical Society established in 1969. It publishes meetings of the society, obituaries of its members, and scholarly articles...
  
   – (publication) Bulletin of the American Astronomical Society
• BAC – (catalog) Bordeaux Astrographic Catalog
• BAO – (organization) Beijing Astronomical Observatory
• BASIS – (observing program) Burst and All Sky Imaging Survey
• BAT – (instrumentation) Burst Alert Telescope, an instrument on SWIFT
  Swift Gamma-Ray Burst Mission
  The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on 20 November 2004, 17:16:00 UTC on a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international...
  
  
• BATC – (observing program) Beijing-Arizona-Taiwan-Connecticut, the name of a multi-wavelength sky survey
• BATSE – (instrument) Burst and Transient Source Experiment, an instrument on the Compton Gamma-Ray Observatory
• BATTeRS – (telescope) Bisei Asteroid Tracking Telescope for Rapid Survey
• BB
  Black body
  A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...
  
   – (astrophysics terminology) Black Body
• BBXRT
  Broad Band X-ray Telescope
  The Broad Band X-ray Telescope was flown on the space shuttle Columbia on 1990 December 2-December 11, as part of the ASTRO-1 payload...
  
   – (telescope) Broad Band X-Ray Telescope
• BCD – (celestial object) Blue Compact Dwarf
• BCD – (software) Basic Calibrated Data, data produced after basic processing
• BCEP
  Beta Cephei variable
  Beta Cephei variables are variable stars which exhibit variations in their brightness due to pulsations of the stars' surfaces. The point of maximum brightness roughly corresponds to the maximum contraction of the star. Typically, Beta Cephei variables change in brightness by 0.01 to 0.3...
  
   – (celestial object) Beta CEPhei, a class of pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s for which Beta Cephei
  Beta Cephei
  Beta Cephei is a third magnitude star in the constellation Cepheus. It has the traditional name Alfirk , meaning "The Flock" This star, along with α Cep and η Cep , were Al Kawākib al Firḳ , meaning "the Stars of The Flock" by Ulug Beg...
  
   is the archetypal object
  • also BCE
• BCG – (celestial object) Blue Compact Galaxy, another name for a blue compact dwarf, also Bright Central Galaxy
• BCG
  Brightest cluster galaxy
  Brightest cluster galaxy is defined as the brightest galaxy in a cluster of galaxies. BCGs include the most massive galaxies in the universe. They are generally elliptical galaxies which lie close to the geometric and kinematical center of their host galaxy cluster, hence at the bottom of the...
  
   – (celestial object) Brightest Cluster Galaxy, the brightest galaxy in a cluster of galaxies
• BCVS – (catalog) Bibliographic Catalogue of Variable Stars
• BD – (catalog) Bonner Durchmusterung
• BD
  Brown dwarf
  Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
  
   – (celestial object) Brown Dwarf
• BEN – (catalog) Jack Bennett catalog, a catalog of deep-sky objects for amateur astronomers
• BEL – (celestial object) broad emission line clouds in Active galactic nucleus
  Active galactic nucleus
  An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
  
  
• BF – (astrophysics terminology) Broadening Function
• BH
  Black hole
  A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
  
   – (celestial object) Black Hole
• BHB – (celestial object) Blue Horizontal Branch, a description for a type of luminous star
• BHC
  Black hole
  A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
  
   – (celestial object) Black Hole Candidate
• BHXRT – (celestial object) Black Hole X-Ray Transient
  • also BHXT
• BIMA
  Berkeley-Illinois-Maryland Association
  The Berkeley-Illinois-Maryland Association was a collaboration of the Universities of California, Illinois, and Maryland that built and operated the eponymously named BIMA radio telescope array. Originally the premier imaging instrument in the world at millimeter wavelengths, the array was...
  
   – (organization & telescope) Berkeley-Illinois-Maryland Association, and also B-M-I Array, microwave
  Microwave
  Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
  
   telescope it operated
• BIS
  British Interplanetary Society
  The British Interplanetary Society founded in 1933 by Philip E. Cleator, is the oldest space advocacy organisation in the world whose aim is exclusively to support and promote astronautics and space exploration.-Structure:...
  
   – (organization) British Interplanetary Society
• BITP – (organization) – Bogolyubov Institute for Theoretical Physics, a Ukrainian research institute
• BLLAC
  BL Lac object
  A BL Lacertae object or BL Lac object is a type of active galaxy with an active galactic nucleus and is named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and large-amplitude flux variability and significant optical...
  
   – (celestial object) BL LACertae, a class of active galaxies for which BL Lacertae
  BL Lacertae
  BL Lacertae or BL Lac is a highly variable, extragalactic AGN . It was first discovered by Cuno Hoffmeister in 1929, but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation...
  
   is the archetypal object
  • also BLL
• BLAST
  BLAST (telescope)
  The Balloon-borne Large Aperture Submillimeter Telescope is a submillimeter telescope that hangs from a high altitude balloon. It has a 2 meter primary mirror that directs light into bolometer arrays operating at 250, 350, and 500 µm. These arrays were developed for the SPIRE instrument on the...
  
   – (telescope) – Balloon-borne Large Aperture Submillimeter Telescope
• BNSC
  British National Space Centre
  The British National Space Centre was a British government body that coordinated civil space activities for the UK. It was replaced on 1 April 2010 by the UK Space Agency.-Structure:...
  
   – (organization) British National Space Centre, the older name for UKSA
  UK Space Agency
  The UK Space Agency is a United Kingdom government agency responsible for its civil space programme. It was established on 1 April 2010 to replace the British National Space Centre and took over responsibility for government policy and key budgets for space and represents the UK in all negotiations...
  
  
• BOAO – (observatory) Bohyunsan Optical Astronomy Observatory, in Korea
• BPM – (catalog) Bruce Proper Motion
• BSG
  Blue supergiant
  Blue supergiants are supergiant stars of spectral type O or B.They are extremely hot and bright, with surface temperatures of 30,000-50,000 K. They typically have 10 to 50 solar masses on the Hertzsprung-Russell diagram, and can have radii up to about 25 solar radii...
  
   – (celestial object) Blue Super Giant
• BSS
  Blue straggler
  Blue stragglers are main sequence stars in open or globular clusters that are more luminous and bluer than stars at the main sequence turn-off point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3...
  
   – (celestial object) Blue Straggler Star
  • also BS
• BSS – (observing program) Bigelow Sky Survey
• BY
  BY Draconis variable
  BY Draconis variables are main sequence variable stars of late spectral types, usually K or M. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in their luminosity due to rotation of the star coupled with star spots, and other...
  
   – (celestial object) BY Draconis, a class of rotating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s for which BY Draconis
  BY Draconis
  BY Draconis is a multi-star system in the constellation Draco. It consists of at least three components. Components A and B form a close binary star system with a short orbital period of only 5.98 days. These may be pre-main sequence objects that are still in the process of collapsing. Their...
  
   is the archetypal object

C

• C - Cambridge Catalog, 2C (Second Cambridge Catalog), 3C (Third Cambridge Catalog)
• CADC – (organization) Canadian Astronomy Data Centre
• CAHA
  Calar Alto Observatory
  The Calar Alto Observatory is an astronomical observatory owned and operated jointly by the Max-Planck-Institut für Astronomie in Heidelberg, Germany, and the Instituto...
  
   – (organization) Centro Astronómico Hispano Alemán, a German-Spanish Astronomical Centre
• CANDELS – (survey) Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey or Cosmic Assembly and Dark Energy Legacy Survey
• CAPS – (instrumentation) CAssini Plasma Spectrometer, an instrument on the Cassini spacecraft
• CARA – (organization) California Association for Research in Astronomy
• CARA – (organization) Center for Astrophysical Research in Antarctica
• CASCA
  Canadian Astronomical Society
  The Canadian Astronomical Society is a Canadian society of professional astronomers, founded in 1971 and incorporated in 1983. The society is devoted to the promotion and advancement of knowledge of the universe through research and education, and its membership is open to people with a...
  
   – (organization) Canadian Astronomical Society / Société canadienne d'astronomie (the name is officially bilingual)
• CASS – (organization) Center for Advanced Space Studies
• CBR – (celestial object) Cosmic Background Radiation
• CC – (celestial object) Candidate Companion, a newly detected observed object that initially appears to orbit another celestial object
• CCD
  Charge-coupled device
  A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
  
   – (instrumentation) Charge Coupled Device
• CCD
  Color-color diagram
  In astronomy, color–color diagrams are a means of comparing the apparent magnitudes of stars at different wavelengths. Astronomers typically observe at narrow bands around certain wavelengths, and objects observed will have different brightnesses in each band. The difference the brightness in two...
  
   – (astrophysics terminology) – Color-Color Diagram, a plot that compares the differences between magnitudes in different wave bands
• CCDM – (catalog) Catalog of Components of Double and Multiple Stars
• CCO – (catalog) Catalogue of Cometary Orbits
• CCO – (celestial object) Central Compact Object, a compact star
  Compact star
  In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
  
   in the center of a planetary nebulae
• CCS
  Carbon star
  A carbon star is a late-type star similar to a red giant whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds,...
  
   – (celestial object) Cool Carbon Star
• CD – (catalog) Cordoba Durchmusterung
• CDIMP – (catalog) Catalogue of Discoveries and Identifications of Minor Planets
• CDM
  Cold dark matter
  Cold dark matter is the improvement of the big bang theory that contains the additional assumption that most of the matter in the Universe consists of material that cannot be observed by its electromagnetic radiation and whose constituent particles move slowly...
  
   – (astrophysics terminology) Cold Dark Matter, used to describe models for structure formation in the universe that include "cold" particles such as WIMPs as dark matter
  Dark matter
  In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
  
  
• CDS
  Centre de Données astronomiques de Strasbourg
  The Centre de données astronomiques de Strasbourg is a data hub which collects and distributes astronomical information. It was established in 1972 under the name Centre de Données Stellaires...
  
   – (organization) Centre de Données astronomiques de Strasbourg
• CELT
  Thirty meter telescope
  The Thirty Metre Telescope is a proposed ground-based large segmented mirror reflecting telescope to be built on Mauna Kea in Hawaii. The telescope is designed for observations from the near-ultraviolet to the mid-infrared . An adaptive optics system would correct for image blur caused by the...
  
   – (telescope) – California Extremely Large Telescope, an older name for the Thirty Meter Telescope
• CEMP – (celestial object) Carbon-Enhanced Metal-Poor, a type of carbon star
  Carbon star
  A carbon star is a late-type star similar to a red giant whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds,...
  
  
  • CEMP-no – (celestial object) Carbon-Enhanced Metal-Poor star with no enhancement of elements produced by the r-process
    R-process
    The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
    
     or s-process
    S-process
    The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...
    
     nucleosynthesis
    Nucleosynthesis
    Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
    
    
  • CEMP-r – (celestial object) Carbon-Enhanced Metal-Poor star with an enhancement of elements produced by r-process
    R-process
    The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
    
     nucleosynthesis
    Nucleosynthesis
    Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
    
    
  • CEMP-s – (celestial object) Carbon-Enhanced Metal-Poor star with an enhancement of elements produced by s-process
    S-process
    The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...
    
     nucleosynthesis
    Nucleosynthesis
    Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
    
    
  • CEMP-r/s – (celestial object) Carbon-Enhanced Metal-Poor star with an enhancement of elements produced by both r-process
    R-process
    The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
    
     and s-process
    S-process
    The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...
    
     nucleosynthesis
    Nucleosynthesis
    Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
    
    
• CEP – (celestial object) CEPheid, a type of pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  
• CEPS
  Center for Earth and Planetary Studies
  The Center for Earth and Planetary Studies is a research institute affiliated with the Smithsonian Institution. Based in Washington, DC, the Center, which was founded in 1972, conducts scientific research related to planetary science, geophysics and the biophysical environment...
  
   – (organization) Center for Earth and Planetary Studies
• CfA – (organization) Center for Astrophysics
• CFHT
  Canada-France-Hawaii Telescope
  The Canada–France–Hawaii Telescope is located near the summit of Mauna Kea mountain on Hawaii's Big Island at an altitude of 4,204 meters , and is one of the observatories that comprise the Mauna Kea Observatory...
  
   – (telescope) Canada-France-Hawaii Telescope
• CFRS – (observing program), Canada-France Redshift Survey
• CG – (astrophysics terminology) Center of Gravity
• CG – (celestial object) Cometary Globule, a Bok globule
  Bok globule
  Bok globules are dark clouds of dense cosmic dust and gas in which star formation sometimes takes place. Bok globules are found within H II regions, and typically have a mass of about 2 to 50 solar masses contained within a region about a light year or so across...
  
   that show signs of a tail-like extension
• CG – (celestial object) Compact Galaxy
• CGCS
  Carbon star
  A carbon star is a late-type star similar to a red giant whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds,...
  
   – (celestial object) Cool Galactic Carbon Star
• CGRO
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
   – (telescope) Compton Gamma Ray Observatory
• CGSS – (catalog) Catalogue of Galactic S Stars
• CHARA – (organization) Center for High Angular Resolution Astronomy
• CIAO – (software) Chandra Interactive Analysis of Observations, software for processing Chandra X-ray Observatory
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
   data
• CIAO – (instrumentation) Coronagraphic Imager with Adaptive Optics, an instrument for the Subaru Telescope
• CIBR – (celestial object) Cosmic Infrared Background Radiation
  • also CIB
• CIDA – (instrumentation) Cometary Interplanetary Dust Analyzer, an instrument on the Stardust
  Stardust (spacecraft)
  Stardust is a 300-kilogram robotic space probe launched by NASA on February 7, 1999 to study the asteroid 5535 Annefrank and collect samples from the coma of comet Wild 2. The primary mission was completed January 15, 2006, when the sample return capsule returned to Earth...
  
   spacecraft
• CINEOS – (observing program) Campo Imperatore Near-Earth Object Survey
• CIO – (catalog) Catalog of Infrared Observations
• CISCO – (instrumentation) Cooled Infrared Spectrograph and Camera for OHS, an instrument for the Subaru Telescope
• CM – (astrophysics terminology) Center of Mass
• CMBR – (celestial object) Cosmic Microwave Background Radiation
  • also CMB, CBR, MBR
• CMC – (catalog) Carlsberg Meridian Catalogue
• CMD – (astrophysics terminology) Color-Magnitude Diagram, commonly used to describe the Hertzsprung-Russell diagram or similar diagrams
  • also CM
• CNB
  Cosmic neutrino background
  The cosmic neutrino background is the universe's background particle radiation composed of neutrinos.Like the cosmic microwave background radiation , the CνB is a relic of the big bang, and while the CMB dates from when the universe was 379,000 years old, the CνB decoupled from matter when the...
  
   – (celestial object) Cosmic Neutrino Background
• CNES
  CNES
  The is the French government space agency . Established under President Charles de Gaulle in 1961, its headquarters are located in central Paris and it is under the supervision of the French Ministries of Defence and Research...
  
   – (organization) Centre Nationale d'Etudes Spatiales, the French Space Agency
• CNO – (astrophysics terminology) Carbon-Nitrogen-Oxygen, a sequence of nuclear fusion processes
• CNR
  Consiglio Nazionale delle Ricerche
  The Consiglio Nazionale delle Ricerche or National Research Council, is an Italian public organization set up to support scientific and technological research. Its headquarters are in Rome.-History:The institution was founded in 1923...
  
   – (organization) Consiglio Nazionale delle Ricerche
• CNSR – (spacecraft) Comet Nucleus Sample Return
• COBE – (telescope) Cosmic Background Explorer, a space telescope used to study the cosmic microwave background radiation
  Cosmic microwave background radiation
  In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
  
  
• COHSI – (instrumentation) Cambridge OH-Suppression Instrument
• Col – (catalog) Collinder catalog
  Collinder catalog
  In astronomy, the Collinder catalog is a catalog of open clusters by Swedish astronomer Per Collinder. It was published in 1931 as an appendix to Collinder's paper On structural properties of open galactic clusters and their spatial distribution. Catalog objects may be denoted as Col + catalog...
  
  
• COMICS – (instrumentation) COoled Mid-Infrared Camera and Spectrometer, an instrument for the Subaru Telescope
• CGRO
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
   – (telescope) COMPton TELescope, another name for the Compton Gamma Ray Observatory
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
  
• COROT
  Corot (space mission)
  COROT is a space mission led by the French Space Agency in conjunction with the European Space Agency and other international partners...
  
   – (telescope) COnvection ROtation and planetary Transits, a space telescope for detecting extrasolar planet
  Extrasolar planet
  An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
  
  s
• COSPAR – (organization) COmmittee on SPAce Research
• COSTAR – (instrumentation) Corrective Optics Space Telescope Axial Replacement, corrective optics for the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• CP – (astrophysics terminology) Chemically Peculiar, a description for stars with peculiar
  Peculiar star
  In astrophysics, peculiar stars have distinctly unusual metal abundances, at least in their surface layers.Chemically peculiar stars are common among hot main sequence stars...
  
   chemical compositions
• CPD – (catalog) Cape Photographic Durchmusterung
• CRAF
  Comet Rendezvous Asteroid Flyby
  The Comet Rendezvous Asteroid Flyby was a cancelled plan for a NASA led exploratory mission designed by the Jet Propulsion Laboratory during the mid-to-late 1980s and early 1990s, that planned to send a spacecraft to encounter an asteroid, and then to rendezvous with a comet and fly alongside it...
  
   – (spacecraft) Comet Rendezvous Asteroid Flyby
• CSA – (organization) Canadian Space Agency
• CSBN – (organization) Committee for Small-Body Nomenclature
• CSE
  Circumstellar envelope
  Circumstellar envelope is the part of the star,having roughly spherical shape and not gravitationally bound to the star core.Usually circumstellar envelopes are formed from the dense stellar wind or presentbefore formation of the star...
  
  - (celestial object) Circumstellar Envelope, structural descriptions of a planetary nebula
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
  
• CSI – (catalog) Catalog of Stellar Identification, a compilation of the catalogs, BD, CD, and CPD
• CSO
  Caltech Submillimeter Observatory
  The Caltech Submillimeter Observatory is a diameter submillimeter wavelength telescope situated alongside the James Clerk Maxwell Telescope at Mauna Kea Observatory. It is engaged in submillimeter astronomy, of the terahertz radiation band.The CSO and JCMT were combined to form the first...
  
   – (telescope) Caltech Submillimeter Observatory
• CSPN – (celestial object) Central Star of Planetary Nebula
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
  
  • also CSPNe (plural form of CSPN)
• CSS – (observing program) Catalina Sky Survey
• CST – (astrophysics terminology) ConStanT, used to describe non-variable stars
• CSV – (catalog) Catalog of Suspected Variables
• CTIO – (telescope/organization) Cerro Tololo Interamerican Observatory
• CTTS – (celestial object) Classical T-Tauri
  T Tauri
  T Tauri is a variable star in the constellation Taurus, the prototype of the T Tauri stars. It was discovered in October 1852 by John Russell Hind...
  
   Star
• CV – (celestial object) Cataclysmic Variable, a type of variable
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
   binary
  Binary star
  A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
  
   star system
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
   that contains a white dwarf
  White dwarf
  A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
  
   and a companion star that changes
• CW
  W Virginis variable
  W Virginis variables are a subclass of Type II Cepheids which exhibit pulsation periods between 10–20 days, and are of spectral class F6 – K2.They were first recognized as being distinct from classical Cepheids by Walter Baade in 1942, in a study of Cepheids in the Andromeda Galaxy that proposed...
  
   – (celestial object) Cepheid W Virginis, a class of Cepheids named after W Virginis, the archetype for the class
  • CWA – (celestial object) Cepheid W Virginis A, a subclass of CW stars that that vary in brightness on timescales of less than 8 days
  • CWB – (celestial object) Cepheid W Virginis B, a subclass of CW stars that vary in brightness on timescales greater than 8 days
• CXBR – (celestial object) Cosmic X-ray Background Radiation
• CXO – (catalog) Chandra X-ray Observation, a catalog based from the Chandra
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
   space telescope

D

• DAO
  Dominion Astrophysical Observatory
  The Dominion Astrophysical Observatory, located on Observatory Hill, in Saanich, British Columbia, was completed in 1918 by the Canadian government. Proposed and designed by John S...
  
   – (organization) Dominion Astrophysical Observatory
• DCEP – (celestial object) Delta CEPhei, a class of Cepheids named after Delta Cephei
  Delta Cephei
  Delta Cephei is a binary star system approximately 891 light-years away in the constellation of Cepheus . Delta Cephei is the prototype of the Cepheid variable stars, and it is among the closest stars of this type to the Sun...
  
  , the archetype for the class
• DDEB – (celectial object) Double-lined eclipsing binary
• DENIS – (observing program/catalog) DEep Near Infrared Survey
• DENIS-P – (catalog) DEep Near Infrared Survey, Provisory designation [or also known as DNS].
• DES – (observing program) Dark Energy Survey
• DES
  Deep Ecliptic Survey
  The Deep Ecliptic Survey is a project to find Kuiper belt objects , using the facilities of the National Optical Astronomy Observatory .The principal investigator is Bob Millis....
  
   – (observing program) Deep Ecliptic Survey
• DIB
  Diffuse interstellar band
  Diffuse interstellar bands are absorption features seen in the spectra of astronomical objects in our galaxy. They are caused by the absorption of light by the interstellar medium...
  
   – (celestial object) Diffuse Interstellar Band, an absorption feature in stellar spectra
  Spectrum
  A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
  
   with an interstellar origin
• DIRBE
  Diffuse Infrared Background Experiment
  Diffuse Infrared Background Experiment was an experiment on NASA's COBE mission, to survey the diffuse infrared sky. The DIRBE instrument was an absolute radiometer with an off-axis folded-Gregorian reflecting telescope, with 19 cm diameter aperture...
  
   – (instrumentation) Diffuse InfraRed Background Experiment, a multiwavelength infrared detector used to map dust emission
• DISR – (instrumentation) – Descent Imager/Spectral Radiometer, an instrument on the Huygens probe
  Huygens probe
  The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
  
  
• DMR – (instrumentation) Differential Microwave Radiometer, a microwave instrument that would map variations (or anisotropies) in the CMB
• DN
  Dwarf nova
  A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
  
   – (celestial object) Dwarf Nova
• DNS – (celestial object) Double Neutron Star
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
  , another name for a binary neutron star system. [Caution: Do not confuse with DNS relating to DENIS – Deep Near Infrared Survey].
• DPOSS – (data) Digitized Palomar Observatory Sky Survey
• DS
  Dwarf star
  The term dwarf star refers to a variety of distinct classes of stars.* Dwarf star alone generally refers to any main sequence star, a star of luminosity class V.** Red dwarfs are low-mass main sequence stars....
  
   – (celestial object) Dwarf Star
• DSCT
  Delta Scuti variable
  A Delta Scuti variable is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface. Typical brightness fluctuations are from 0.003 to 0.9 magnitudes in V over a period of a few hours, although the amplitude and period of the...
  
   – Delta SCuTi, a class of pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after Delta Scuti
  Delta Scuti
  Delta Scuti is a white, F-type giant star in the constellation Scutum. It is approximately 187 light years from Earth. Delta Scuti is the prototype of the Delta Scuti type variable stars. It is a high-amplitude δ Scuti type pulsator with light variations of about 0.15 minutes...
  
  , the archetype for the class
• DSN
  Deep Space Network
  The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
  
   – (communications network) Deep Space Network, a network of radio antennas used for communicating to spacecraft
  Spacecraft
  A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
  
  
• DSS
  Digitized Sky Survey
  The Digitized Sky Survey is a digital version of several photographic atlases of the night sky, and an ongoing project to produce more digital versions of photographic astronomical datasets.- Versions and source material :...
  
   – (data) Digitized Sky Survey
• DWE – (instrumentation) – Doppler Wind Experiment, an instrument on the Huygens probe
  Huygens probe
  The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
  
  

E

• E
  Binary star
  A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
  
   – (celestial object) Eclipsing, used to describe a binary star system
  Binary star
  A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
  
   with variable
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
   brightness in which the stars eclipse each other
  • EA – (celestial object) Eclipsing Algol, a class of eclipsing binary star
    Binary star
    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
    
    s named after Algol, the archetype for the class
  • EB – (celestial object) Eclipsing Beta Lyrae, a class of eclipsing binary star
    Binary star
    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
    
    s named after Beta Lyrae
    Beta Lyrae
    Beta Lyrae is a binary star system approximately 882 light-years away in the constellation Lyra. Beta Lyrae has the traditional name Sheliak , from الشلياق šiliyāq, the Arabic name of the constellation Lyra.Beta Lyrae is an eclipsing semi-detached binary system made up of a B7II primary star and...
    
    , the archetype for the class
  • EW – (celestial object) Eclipsing W Ursa Majoris, a class of eclipsing binary star
    Binary star
    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
    
    s named after W Ursa Majoris, the archetype for the class
• EAAE
  EAAE – European Association for Astronomy Education
  The ', is a non-profit European organization for the promotion of science education in general, and of astronomy in particular.The Organization was founded on November 25, 1995, in Athens, as a result of the Declaration of the EU/ESO workshop on Teaching of Astronomy in Europe's Secondary...
  
   – (organization) European Association for Astronomy Education
• E-ELT – (telescope) – European Extremely Large Telescope
• EAPSNET
  East-Asian Planet Search Network
  East-Asian Planet Search Network, , is an international collaboration between Korea, China and Japan. Each facility, BOAO , Xinglong , and OAO , has a 2m class telescope, a high dispersion echelle spectrograph, and an iodine absorption cell for precise RV measurements, looking for extrasolar...
  
   – (organization) – East-Asian Planet Search Network
• EC – (celestial object) Embedded Cluster, a star cluster that is partially or fully embedded in interstellar gas or dust
  Cosmic dust
  Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
  
  
• ECA – (celestial object) Earth Crossing Asteroid
• EGG – (celestial object) Evaporating Gaseous Globule
• EGGR – (catalog) Eggen & Greenstein, a catalog of mostly white dwarf
  White dwarf
  A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
  
  s
• EGP – (celestial object) Extrasolar Giant Planet
  Extrasolar planet
  An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
  
  
• EGRET
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
   – (telescope) Energetic Gamma Ray Experiment Telescope, another name for the Compton Gamma Ray Observatory
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
  
• EHB – (celestial object) Extreme Horizontal Branch, the description for a type of hot, evolved star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  
• EJASA – (publication) Electronic Journal of the Astronomical Society of the Atlantic
• EKBO – (celestial object) Edgeworth-Kuiper Belt Object, an alternative name for Kuiper Belt Objects
• ELIAS – (observing program) European Large Area ISO Survey, a survey of high redshift
  Redshift
  In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
  
   galaxies performed with the Infrared Space Observatory (ISO)
  Infrared Space Observatory
  The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency , in cooperation with ISAS and NASA...
  
  
• ELT
  Extremely large telescope
  An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
  
   – (telescope) Extremely Large Telescope
• EMP – (catalog) Ephemerides of Minor Planets
• EMP – (celestial object) Extremely Metal-Poor, a description for stars that contain few elements other than hydrogen
  Hydrogen
  Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
  
   and helium
  Helium
  Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
  
  
• ENACS – (observing program) ESO Nearby Abell Cluster Survey, a survey of galaxy cluster
  Galaxy cluster
  A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...
  
  s
• ERO – (celestial object) Extremely Red Object, a name applied to galaxies with red spectra
  Spectrum
  A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
  
  
• ESA
  European Space Agency
  The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
  
   – (organization) European Space Agency
• ESO
  European Southern Observatory
  The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
  
   – (organization) European Southern Observatory
• ESTEC
  European Space Research and Technology Centre
  The European Space Research and Technology Centre is the European Space Agency's main technology development and test centre for spacecraft and space technology. It is situated in Noordwijk, South Holland, in the western Netherlands....
  
   – (organization) European Space research and TEchnology Centre
• ESTRACK
  ESTRACK
  The European Space Operations Centre operates a number of ground-based space-tracking stations for the European Space Agency known as the European Space Tracking network. The stations support various ESA spacecraft and facilitate communications between ground operators and scientific probes such...
  
   – (communications network) European Space TRACKing, a network of radio antennas used for communicating to spacecraft
  Spacecraft
  A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
  
  
• EUV
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   – (astrophysics terminology) Extreme UltraViolet
• EUVE
  Extreme Ultraviolet Explorer
  The Extreme Ultraviolet Explorer was a space telescope for ultraviolet astronomy, launched on June 7, 1992. With instruments for UV radiation between wavelengths of 7 and 76 nm, the EUVE was the first satellite mission especially for the short-wave ultraviolet range...
  
   – (telescope) Extreme UltraViolet Explorer, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   space telescope
• EVN
  European VLBI Network
  The European VLBI Network was formed in 1980 by a consortium of five of the major radio astronomy institutes in Europe . Since 1980, the EVN and the Consortium has grown to include 9 institutes with 12 radio telescopes in 8 western European countries as well as associated institutes with...
  
   – (organization) European VLBI Network

F

• FAME
  Full-sky Astrometric Mapping Explorer
  Full-sky Astrometric Mapping Explorer was a proposed astrometric satellite designed to determine with unprecedented accuracy the positions, distances, and motions of 40 million stars within our galactic neighborhood...
  
   – (telescope) Full-sky Astrometric Mapping Explorer
• FASTT – (telescope) Flagstaff Astrometric Scanning Transit Telescope
• FCC – (catalog) Fornax Cluster Catalog, a catalog of galaxies in the Fornax Cluster
  Fornax Cluster
  At a distance of approximately 62.0 Mly , the Fornax Cluster is the second richest cluster of galaxies within 100 million light-years, although it is much smaller than the Virgo Cluster. It lies primarily in the constellation Fornax, and may be associated with the nearby Eridanus Group...
  
  
• FEB – (celestial object) Falling-Evaporating Body, a solid planetary object that is being evaporated by the stellar wind
• FGS – (instrumentation) Fine Guidance Sensors, an instrument on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• FHST – (instrumentation) Fixed Head Star Trackers, an instrument on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• FIR
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   – (astrophysics terminology) Far InfraRed
• FIRST – (observing program) Faint Images of the Radio Sky at Twenty-centimeters, a radio survey of the sky with the Very Large Array
  Very Large Array
  The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...
  
  
• FIRST
  Herschel Space Observatory
  The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....
  
   – (telescope) Far InfraRed and Submillimeter Space Telescope, an older name for the Herschel Space Observatory
  Herschel Space Observatory
  The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....
  
  
• FIRAS – (Instrumentation) Far-InfraRed Absolute Spectrophotometer
• FITS – (software) Flexible Image Transport System, the format commonly used for scientific astronomy images
• FLAMES – (instrumentation) Fibre Large Array Multi Element Spectrograph, instrument on the VLT
  Very Large Telescope
  The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
  
  
• FLOAT – (telescope) Fibre-Linked Optical Array Telescope
• FLWO – (telescope) Fred L. Whipple Observatory
• FMO – (celestial object) Fast Moving Object, a description for asteroid
  Asteroid
  Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
  
  s so close to the Earth that they appear to be moving very fast
• FOC
  Faint Object Camera
  The Faint Object Camera was a camera installed on the Hubble Space Telescope from launch in 1990 until 2002. It was replaced by the Advanced Camera for Surveys.The camera was built by Dornier GmbH and was funded by the European Space Agency...
  
   – (instrumentation) Faint Object Camera, a camera formerly on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• FOCAS – (instrumentation) Faint Object Camera And Spectrograph, an instrument for the Subaru Telescope
• FOS
  Faint Object Spectrograph
  The Faint Object Spectrograph was a spectrograph installed on the Hubble Space Telescope. It was replaced by the Space Telescope Imaging Spectrograph in 1997, and is now on display in the National Air and Space Museum in Washington DC. -FOS facts:...
  
   – (instrumentation) Faint Object Spectrograph, a spectrometer
  Spectrometer
  A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
  
   formerly on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• FOV – (instrumentation) Field Of View
• FRED – (astrophysics terminology) Fast Rise Exponential Decay, used to describe the variations in the luminosity of gamma ray bursts over time
• FSC – (catalog) Faint Source Catalogue, one of the catalogs produced using Infrared Astronomical Satellite data
• FTL – (astrophysics terminology) Faster Than Light
• FUOR – (celestial object) FU Orionis objects, a class of variable
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
   pre–main sequence stars named after FU Orionis
  FU Orionis
  In stellar evolution, an FU Orionis star is a pre–main sequence star which displays an extreme change in magnitude and spectral type. One example is the star V1057 Cyg, which became 6 magnitudes brighter and went from spectral type dKe to F supergiant...
  
  , the archetype for the class
  • also FU
• FUSE
  Far Ultraviolet Spectroscopic Explorer
  The Far Ultraviolet Spectroscopic Explorer is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II rocket on June 24, 1999, as a part of NASA's Origins program...
  
   – (telescope) Far Ultraviolet Spectroscopic Explorer, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   space telescope
• FUVITA – (instrumentation) Far UltraViolet Imaging Telescope Array, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   imager for the Spectrum-Roentgen-Gamma mission
• FWHM – (instrumentation) Full Width at Half Maximum, used to describe telescopes' resolution
• FWZI – (instrumentation) Full Width at Zero Intensity, used to describe telescopes' resolution

G

• G – (catalog) Giclas, a catalog of nearby star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• GAIA
  Gaia probe
  Gaia is a European Space Agency astrometry space mission, and a successor to the ESA Hipparcos mission. It was included within the context of the ESA Horizon 2000 Plus long-term scientific programme in 2000. Arianespace expects to launch Gaia for the ESA in March 2013, using a Soyuz rocket from...
  
   – (telescope) Global Astrometric Interferometer for Astrophysics, a planned space telescope that will be used to make high-precision measurements of stars
• GALEX – (telescope) Galaxy Evolution Explorer, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   space telescope
• GASP – (software) Guide star Astrometric Support Package
• GAT – (catalog) AO (Gatewood+), catalog of G. Gatewood's observations
• GBT
  Green Bank Telescope
  The Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...
  
   – (telescope) Green Bank Telescope
• GC – (catalog) General Catalog, a catalog of clusters, nebulae, and galaxies created by John Herschel
  John Herschel
  Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
  
   and now superseded by the New General Catalogue
  New General Catalogue
  The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
  
  
• GCAS – (celestial object) Gamma CASsiopeiae, a class of eruptive variable stars named after Gamma Cassiopeiae
  Gamma Cassiopeiae
  Gamma Cassiopeiae is an eruptive variable star, whose brightness changes irregularly between +2.20 mag and +3.40 mag. It is the prototype of the Gamma Cassiopeiae variable stars. Although it is a fairly bright star, it has no traditional Arabic or Latin name...
  
  , the archetype for the class
• GCMS – (instrumentation) – Gas Chromatograph and Mass Spectrometer, an instrument on the Huygens probe
  Huygens probe
  The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
  
  
  • also GC/MS
• GCN – (organization) GRB Coordinates Network
• GCR
  Cosmic ray
  Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
  
   – (astrophysics terminology) Galactic Cosmic Rays
• GCVS – (catalog) the General Catalog of Variable Stars
• GD – (catalog) Giclas Dwarf, a catalog of white dwarf
  White dwarf
  A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
  
  
• GDS – (celestial object) Great Dark Spot, a transient feature in the clouds of Neptune
  Neptune
  Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
  
  
• GEM – (observing program) Galactic Emission Mapping
• GEM
  Galileo spacecraft
  Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
  
   – (observing program) Galileo Europa Mission, the description for the science observation program of Europa
  Europa (moon)
  Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
  
   performed by the Galileo spacecraft
  Galileo spacecraft
  Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
  
  
• GEM
  Giotto mission
  Giotto was a European robotic spacecraft mission from the European Space Agency, intended to fly by and study Halley's Comet. On 13 March 1986, the mission succeeded in approaching Halley's nucleus at a distance of 596 kilometers....
  
   – (observing program) Giotto Extended Mission, the description for the extended operations of the Giotto spacecraft
• GEMS – (organization) Group Evolution Multi-wavelength Study
• GEMS – (survey) Galaxy Evolution from Morphology and Spectral energy distributions
• GEMSS – (organization) Global Exoplanet M-dwarf Search-Survey, a search for exoplanets
  Extrasolar planet
  An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
  
   around m-dwarf stars
• GEODDS – (telescope) Ground-based Electro-Optical Deep Space Surveillance, a network of telescopes used in a United States Air Force
  United States Air Force
  The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
  
   program for observing space junk
• GEOS – (organization) Groupe Européen Observations Stellaires, an amateur and professional association for study of variable stars.
• GERLUMPH – (instrumentation) GPU-Enabled, High Resolution MicroLensing Parameter survey, where GPU is an acronym for Graphics Processing Unit.
• GH – (catalog) Giclas Hyades, a catalog of stars in the Hyades cluster
  Hyades (star cluster)
  The Hyades is the nearest open cluster to the Solar System and one of the best-studied of all star clusters. The Hipparcos satellite, the Hubble Space Telescope, and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster's center of ~153 ly...
  
  
• GHRS
  Goddard High Resolution Spectrograph
  The Goddard High Resolution Spectrograph was a spectrograph installed on the Hubble Space Telescope. It was replaced by the Near Infrared Camera and Multi-Object Spectrometer in 1997.-GHRS facts:...
  
   – (instrumentation) Goddard High Resolution Spectrograph, a spectrograph
  Spectrograph
  A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
  
   on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
  • also HRS
• GIA – (organization) Gruppo Italiano Astrometristi
• GIMI – (instrumentation) Global Imaging Monitor of the Ionosphere, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   imager on the Advanced Research and Global Observation Satellite
• GJ – (catalog) Gliese
  Wilhelm Gliese
  Wilhelm Gliese was a German astronomer who specialized in the study and cataloging of nearby stars.-Life:Gliese was born in Goldberg, now in Polish Silesia, the son of judge Wilhelm Gliese. He worked at the Astronomisches Rechen-Institut, first in Berlin and then in Heidelberg...
  
   & Jahreiß/Jahreiss
  Hartmut Jahreiß
  Hartmut Jahreiß is a German astronomer associated with Astronomisches Rechen-Institut specializing in the study of nearby stars.-Work:Hartmut Jahreiß obtained his Ph.D from the University of Heidelberg. His thesis was on the spatial distribution, kinetics and age of stars near the Sun...
  
   nearby star catalog
• GL – (catalog) Gliese
  Wilhelm Gliese
  Wilhelm Gliese was a German astronomer who specialized in the study and cataloging of nearby stars.-Life:Gliese was born in Goldberg, now in Polish Silesia, the son of judge Wilhelm Gliese. He worked at the Astronomisches Rechen-Institut, first in Berlin and then in Heidelberg...
  
   nearby star catalog
• GLAST
  Gamma-ray Large Area Space Telescope
  The Fermi Gamma-ray Space Telescope , formerly referred to as the “Gamma-ray Large Area Space Telescope ”, is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit...
  
   – (telescope) Gamma-ray Large Area Space Telescope
• GLIMPSE – (observing program) Galactic Legacy Infrared Mid-Plane Survey Extraordinaire
• GMC – (celestial object) Giant molecular Cloud
• GMF – (celestial object) Galactic Magnetic Field
• GMRT – (telescope) Giant Meter Radio Telescope
• GMT
  Giant Magellan Telescope
  The Giant Magellan Telescope is a ground-based extremely large telescope planned for completion in 2018. It will consist of seven diameter primary segments, with the resolving power of a primary mirror and collecting area equivalent to one...
  
   – (telescope) – Giant Magellan Telescope, a telescope being built by a US-Australian collaboration
• GONG – (organization) Global Oscillation Network Group, an organization that monitors oscillations in the Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  
• GOODS
  Great Observatories Origins Deep Survey
  The Great Observatories Origins Deep Survey or GOODS is an astronomical survey combining deep observations from three of NASAs Great Observatories: the Hubble Space Telescope, the Spitzer Space Telescope and the Chandra X-ray Observatory along with data from other space-based telescopes, such as...
  
   – (survey) Great Observatories Origins Deep Survey a survey of various redshifts to study galactic formation and evolution
  Galaxy formation and evolution
  The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...
  
  
• GP – (astrophysics terminology) Giant Pulses, a description for a type of observed pulse emission from pulsar
  Pulsar
  A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
  
  s
• GPS – (astrophysics teminology) GHz-Peaked Spectrum, a description for the radio or microwave
  Microwave
  Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
  
   spectra
  Spectrum
  A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
  
   of some galaxies
• GR
  General relativity
  General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
  
   – (astrophysics terminology) General Relativity
• GR – (catalog) Giclas Red dwarf, a catalog of red dwarf
  Red dwarf
  According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
  
  s
• GRB
  Gamma ray burst
  Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
  
   – (celestial object) Gamma Ray Burst
• GRO
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
   – (telescope) Gamma Ray Observatory, another name for the Compton Gamma Ray Observatory
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
  
• GROSCE – (telescope) Gamma Ray Burst Optical Counterparts Search Experiment, an automated telescope used to detect the optical counterparts to gamma ray burst
  Gamma ray burst
  Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
  
  s
• GRS
  Gamma Ray Spectrometer
  Gamma Ray Spectrometer is a gamma-ray spectrometer on the 2001 Mars Odyssey spacecraft, a space probe orbiting the planet Mars since 2001. Part of the United State's NASA's Mars Surveyor Program, it returns geological data about Mars' surface such as identifying elements and the location of water...
  
   – (instrumentation) Gamma Ray Spectrometer, an instrument on the Mars Observer
  Mars Observer
  The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
  
  
• GRS – (celestial object) Great Red Spot, a feature in the clouds of Jupiter
  Jupiter
  Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
  
  
• GSC
  Guide Star Catalog
  The Guide Star Catalog is also known as the Hubble Space Telescope, Guide Catalog . It is a star catalog compiled to support the Hubble Space Telescope with targeting off-axis stars. GSC-I contained approximately 20,000,000 stars with apparent magnitudes of 6 to 15. GSC-II contains 945,592,683...
  
   – (catalog) Guide Star Catalog, a catalog of stars used for pointing the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• GSC2 – (catalog) Guide Star Catalog version 2, a catalog of stars used for pointing the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
  • also GSC II
• GSFC
  Goddard Space Flight Center
  The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
  
   – (organization) Goddard Space Flight Center, a NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
   institution
• GSPC – (catalog) Guide Star Photometric Catalog, a catalog of stars with precisely measured fluxes used to calibrate the Guide Star Catalog
  Guide Star Catalog
  The Guide Star Catalog is also known as the Hubble Space Telescope, Guide Catalog . It is a star catalog compiled to support the Hubble Space Telescope with targeting off-axis stars. GSC-I contained approximately 20,000,000 stars with apparent magnitudes of 6 to 15. GSC-II contains 945,592,683...
  
  
• GTC
  Gran Telescopio Canarias
  The Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
  
   – (telescope) Gran Telescopio Canarias, the 10.4 m reflecting telescope on the island of La Palma
  La Palma
  La Palma is the most north-westerly of the Canary Islands. La Palma has an area of 706 km2 making it the fifth largest of the seven main Canary Islands...
  
  , Canary Islands
  Canary Islands
  The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
  
  , Spain
  Spain
  Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
  
  

H

• HAeBe – (celestial object) Herbig AeBe star, a type of pre–main sequence star with strong spectral emission lines
  Spectral line
  A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
  
  
  • HAe – (celestial object) Herbig Ae star
  • HBe – (celestial object) Herbig Be star
• HALCA
  HALCA
  The HALCA , also known for its project name VSOP , or the code name MUSES-B for the second of the Mu Space Engineering Spacecraft series, is a Japanese 8 meter diameter radio telescope satellite which was used for Very Long Baseline Interferometry...
  
   – (telescope) Highly Advanced Laboratory for Communications and Astronomy, a satellite that is part of the VLBI Space Observatory Program, a Japanese radio astronomy
  Radio astronomy
  Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
  
   project
• HAO
  High Altitude Observatory
  The High Altitude Observatory conducts research and provides support and facilities for the solar-terrestrial research community in the areas of solar and heliospheric physics, and the effects of solar variability on the Earth's magnetosphere, ionosphere, and upper atmosphere.HAO is a laboratory...
  
   – (organization) High Altitude Observatory
• HARPS
  High Accuracy Radial Velocity Planet Searcher
  The High Accuracy Radial velocity Planet Searcher is a high-precision echelle spectrograph installed in 2002 on ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003...
  
   – (instrumentation) High Accuracy Radial velocity Planet Searcher, a high-precision spectrograph
  Spectrograph
  A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
  
   installed on the ESO 3.6m telescope
  ESO 3.6m Telescope
  The ESO 3.6 m Telescope is an optical reflecting telescope run by the European Southern Observatory at La Silla Observatory, Chile since 1977, with a clear aperture of about 3.6 meters and 8.6 m2 area. It received an overhaul in 1999 and a new secondary in 2004...
  
  
• HASI – (instrumentation) Huygens Atmosphere Structure Instrument, an instrument on the Huygens probe
  Huygens probe
  The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
  
  
• HB
  Horizontal branch
  The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
  
   – (celestial object) Horizontal Branch, a description for a type of evolved red giant star
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
   in which helium is burned in the core and hydrogen is burned in a shell around the core
• HBRP – (celestial object) High-magnetic field Radio Pulsar
• HBV – (catalog) Hamburg-Bergedorf Variables, a catalog of variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s
• HBMM – (astrophysics terminology) Hydrogen Burning Minimum Mass
• HCO
  Harvard College Observatory
  The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...
  
   – (organization) Harvard College Observatory
• HCS
  Heliospheric current sheet
  The heliospheric current sheet is the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere. The shape of the current sheet results from the influence of the Sun's...
  
   – (celestial object) Heliospheric Current Sheet, the boundary where the polarity of the Sun's magnetic field changes direction
• HD
  Henry Draper Catalogue
  The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
  
   – (catalog) Henry Draper, a catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• HDE – (catalog) Henry Draper Extension, a catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• HDF
  Hubble Deep Field
  The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
  
   – (data/celestial object) Hubble Deep Field, an area of the sky with little foreground obscuration that was observed deeply with the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  ; also the name for the data product itself
• HDM
  Hot dark matter
  Hot dark matter is a hypothetical form of dark matter which consists of particles that travel with ultrarelativistic velocities. The best candidate for the identity of hot dark matter is the neutrino. Neutrinos have very small masses, and do not take part in two of the four fundamental forces, the...
  
   – (astrophysics terminology) Hot Dark Matter, a description for cosmological models treating neutrino
  Neutrino
  A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
  
  s as dark matter
  Dark matter
  In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
  
  
• HDS – (instrumentation) High Dispersion Spectrograph, a spectrograph
  Spectrograph
  A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
  
   on the Subaru Telescope
• HE
  Hamburg/ESO Survey
  The Hamburg/ESO Survey is an astrometric star catalogue published by the University of Hamburg. The catalog contains stars between magnitudes 13 and 18 covering the Southern extragalactic sky.The stated goals of the catalog are...
  
   – (catalog) Hamburg/ESO Survey
• HEAO – (telescope) High Energy Astronomical Observatory, a series of X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   and gamma ray
  Gamma ray
  Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
  
   space telescopes
• HEASARC – (organization) High Energy Astrophysics Science Archival Research Center, a NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
   organization that deals with X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   and gamma ray
  Gamma ray
  Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
  
   telescope data
• HESS
  High Energy Stereoscopic System
  High Energy Stereoscopic System or H.E.S.S. is a next-generation system of Imaging Atmospheric Cherenkov Telescopes for the investigation of cosmic gamma rays in the 100 GeV and TeV energy range...
  
   – (telescope) High Energy Stereoscopic System, a telescope for detecting cosmic ray
  Cosmic ray
  Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
  
  s
• HETE
  High Energy Transient Explorer
  The High Energy Transient Explorer was an American astronomical satellite with international participation . The prime objective of HETE was to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft...
  
   – (telescope) High Energy Transient Explorer, a space telescope that performs multi-wavelength observations of gamma ray burst
  Gamma ray burst
  Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
  
  s
• HF
  Frequency
  Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
  
   – (astrophysics terminology) High Frequency
• HGA
  High-gain antenna
  A high-gain antenna is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna...
  
   – (instrumentation) High Gain Antenna
• HH
  Herbig-Haro object
  Herbig–Haro objects are small patches of nebulosity associated with newly born stars, and are formed when gas ejected by young stars collides with clouds of gas and dust nearby at speeds of several hundred kilometres per second...
  
   – (celestial object) Herbig-Haro object, objects formed when the ejecta from new star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s collides with the interstellar medium
  Interstellar medium
  In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
  
  
  • also HHO
    Herbig-Haro object
    Herbig–Haro objects are small patches of nebulosity associated with newly born stars, and are formed when gas ejected by young stars collides with clouds of gas and dust nearby at speeds of several hundred kilometres per second...
    
    
• HIC – (catalog) HIPPARCOS Input Catalog, a catalog of data for the first target star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s selected for observation by the Hipparcos
  Hipparcos
  Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
  
   
• HICAT – (catalog) HIPASS catalog, a catalog of HI
  Hydrogen line
  The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...
  
   sources, see also NHICAT
• HID – (astrophysics terminology) – Hardness-Intensity Diagram, a type of color magnitude diagram used in X-ray
  X-ray astronomy
  X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...
  
   and gamma ray astronomy
• HIP
  Hipparcos
  Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
  
   – (catalog) HIPPARCOS, the catalog of data produced by Hipparcos
  Hipparcos
  Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
  
  
• HIPASS
  HIPASS
  The HI Parkes All Sky Survey was an astronomical survey for neutral atomic hydrogen . Data was taken between 1997 and 2002 using the Parkes Observatory. HIPASS covered 71% of the sky and identified 5317 sources emitting HI's signature wavelength...
  
   – (Observing program) HI Parkes All-Sky Survey, survey of HI sources
  Hydrogen line
  The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...
  
  
• HIPPARCOS
  Hipparcos
  Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
  
   – (telescope) HIgh Precision PARallax COllecting Satellite, a space telescope specifically designed to measure distances to star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s using parallax
  Parallax
  Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...
  
  
• HISA – (astrophysical terminology) HI Self-Absorption region
• HK – (catalog) Survey for metal-poor stars based on the strength of CaII H and K absorption lines
• HLIRG – (celestial object) HyperLuminous Infrared Galaxy, a galaxy
  Galaxy
  A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
  
   that is brighter than 10¹³ solar luminosities in the infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
  
• HMC – (instrumentation) Halley Multicolor Camera, an instrument on the Giotto spacecraft
  Giotto mission
  Giotto was a European robotic spacecraft mission from the European Space Agency, intended to fly by and study Halley's Comet. On 13 March 1986, the mission succeeded in approaching Halley's nucleus at a distance of 596 kilometers....
  
  
• HMPO – (celestial object) High-Mass Proto-stellar
  Protostar
  A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...
  
   Object
• HMXB – (celestial object) High-Mass X-Ray Binary, an X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
  -luminous binary system consisting of a compact star
  Compact star
  In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
  
   and a massive star
  Supergiant
  Supergiants are among the most massive stars. They occupy the top region of the Hertzsprung-Russell diagram. In the Yerkes spectral classification, supergiants are class Ia or Ib . They typically have bolometric absolute magnitudes between -5 and -12...
  
  
• HPMS – (celestial object) High Proper Motion Star, a star with high proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  
• HR – (catalog) Hoffleit Bright Star
• HR – (astrophysics terminology) Hertzsprung-Russell, a description for a diagram that compares stars' colors to their luminosities
• HRC-I – (instrumentation) High Resolution Camera, an instrument on the Chandra X-Ray Observatory
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
  
• HRD – (instrumentation) High Rate Detector, an instrument on the Cassini spacecraft
• HRMS
  High Resolution Microwave Survey
  The High Resolution Microwave Survey was a NASA project that was to scan ten million frequencies using radio telescopes. A decade in the making, the objective was to find transmissions from alien intelligences. The primary point of observation for the project was the Arecibo Ionaspheric Observatory...
  
   – (observing program) High Resolution Microwave Survey, a survey for microwave
  Microwave
  Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
  
   signals from extraterrestrial intelligence
• HRI – (instrumentation) High Resolution Imager, an instrument on the ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   telescope
• HSP
  High Speed Photometer
  The High Speed Photometer was a scientific instrument installed on the Hubble Space Telescope. The HSP was designed to measure the brightness and polarity of rapidly varying celestial objects. It could observe in ultraviolet, visible light, and near infrared at a rate of one measurement per 10...
  
   – (instrumentation) High Speed Photometer, an instrument formerly on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• HST
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
   – (telescope) Hubble Space Telescope
• HTRA
  High Time Resolution Astrophysics
  High Time Resolution Astrophysics is a section of astronomy/astrophysics involved in measuring and studying astronomical phenomena in time scales of 1 second and smaller...
  
   – (astrophysics terminology) High Time Resolution Astrophysics, a term used to describe the observations of phenomena that vary on timescales of one second or less
• HUT
  Hopkins Ultraviolet Telescope
  The Hopkins Ultraviolet Telescope was a space telescope designed to make spectroscopic observations in the far-ultraviolet region of the electromagnetic spectrum...
  
   – (telescope) Hopkins Ultraviolet Telescope, an ultraviolet telescope that operated from the cargo bay of the Space Shuttle
  Space Shuttle
  The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
  
  
• HVC – (celestial object) High Velocity Cloud, an interstellar cloud with a velocity that is too high to be explained by galactic rotation
• HXD
  HxD
  HxD is a hex editor and disk editor developed by Maël Hörz for Windows. It can open files larger than 4 GiB and open and edit the raw contents of disk drives, as well as display and edit the memory used by running processes...
  
   – (instrumentation) Hard X-ray Detector, an instrument on the Suzaku
  ASTRO-E
  Suzaku is a Japanese X-ray astronomy satellite launched on 10 July 2005 aboard the M-V-6 rocket. The project was renamed Suzaku after its successful launch after the mythical Vermilion bird of the South....
  
   space telescope
• HVS – (celestial object) Hypervelocity Star or High Velocity Star

I

• IAC
  Instituto de Astrofísica de Canarias
  The Instituto de Astrofísica de Canarias is an astrophysical research institute located in Tenerife in the Canary Islands, Spain. It was founded in 1975 at the University of La Laguna.It operates two astronomical observatories in the Canary Islands:...
  
   – (organization) Instituto de Astrofisica de Canarias
• IAPPP – (organization) International Amateur/Professional Photoelectric Photometry
• IAS – (organization) Istituto di Astrofisica Spaziale
• IASY – (observing program) International Active Sun Year, the name given to a series of coordinated Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  -related observational programs performed in 1969 and 1971
• IAU
  International Astronomical Union
  The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
  
   – (organization) International Astronomical Union
• IAUC
  IAU Circular
  The International Astronomical Union Circulars are notices that give information about astronomical phenomena. IAUCs are issued by the IAU's Central Bureau for Astronomical Telegrams at irregular intervals for the discovery and follow-up information regarding such objects as planetary...
  
   – (publication) IAU Circular
• IAYC
  International Astronomical Youth Camp
  The International Astronomical Youth Camp is an annual summer camp for young people with an interest in astronomy. Established in 1969, the IAYC has taken place in over 30 different places in Europe, North Africa and the Near East...
  
   – (meeting) International Astronomical Youth Camp
• IBAS – (instrumentation) – INTEGRAL Burst Alert System, an instrument on the INTEGRAL
  INTEGRAL
  The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
  
   satellite
• IBIS – (instrumentation) – Imager on Board the INTEGRAL Satellite, an instrument on the INTEGRAL
  INTEGRAL
  The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
  
   satellite
• IBVS – (publication) Information Bulletin on Variable Stars
• IC
  Index Catalogue
  The Index Catalogue —also known as the Index Catalogue of Nebulae, the Index Catalogue of Nebulae and Clusters of Stars, IC I, or IC II— is a catalogue of galaxies, nebulae and star clusters that serves as a supplement to the New General Catalogue...
  
   – (catalog) Index Catalog
• IC – (celestial object) Intracluster, a general term to describe either the regions between stars in star cluster
  Star cluster
  Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...
  
  s or the region between galaxies in galaxy cluster
  Galaxy cluster
  A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...
  
  s
• ICE – (spacecraft) International Comet Explorer
• ICM
  Intracluster medium
  In astronomy, the intracluster medium is the superheated plasma present at the center of a galaxy cluster. This is gas heated to temperatures of between roughly 10 and 100 megakelvins and consisting mainly of ionised hydrogen and helium, containing most of the baryonic material in the cluster...
  
   – (celestial object) Intracluster Medium, is the superheated gas present at the center of a galaxy cluster
• ICQ – (publication) International Comet Quarterly
• ICRF
  International Celestial Reference Frame
  The International Celestial Reference Frame is a quasi-inertial reference frame centered at the barycenter of the Solar System, defined by the measured positions of 212 extragalactic sources . Although relativity implies that there is no true inertial frame, the extragalactic sources used to...
  
   – (astrophysics terminology) International Celestial Reference Frame, a coordinate system based on radio sources used to define the locations of objects in the sky
• ICRS
  International Celestial Reference System
  The International Celestial Reference System is the current standard celestial reference system adopted by the International Astronomical Union . Its origin is at the barycenter of the solar system, with axes that are intended to be "fixed" with respect to space...
  
   – (astrophysics terminology) International Celestial Reference System, a coordinate system based on Hipparcos
  Hipparcos
  Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
  
   observations used to define the locations of objects in the sky
• IDA
  International Dark-Sky Association
  The International Dark-Sky Association is a U.S.-based non-profit organization incorporated in 1988 by founders Dr. David Crawford, a professional astronomer, and Dr. Timothy Hunter, a medical doctor/amateur astronomer...
  
   – (organization) International Dark-Sky Association, an organization that seeks to control light pollution
  Light pollution
  Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
  
  
• IDP
  Cosmic dust
  Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
  
   – (celestial object) Interplanetary Dust Particle, dust particles around planets or planetary bodies
• IDS – (catalog) Index catalog of Double Stars
• IEO – (astrophysics terminology) Inner-Earth Object, used to describe the orbits of asteroid
  Asteroid
  Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
  
  s
• IERS – (organization) International Earth Rotation geophysical Service or International Earth rotation and Reference systems Service, an organization that monitors the Earth's orientation with respect to the radio sources used to define the ICRF
  International Celestial Reference Frame
  The International Celestial Reference Frame is a quasi-inertial reference frame centered at the barycenter of the Solar System, defined by the measured positions of 212 extragalactic sources . Although relativity implies that there is no true inertial frame, the extragalactic sources used to...
  
  
• IfA
  Institute for Astronomy
  The Institute for Astronomy is a research unit within the University of Hawaii system, led by Günther Hasinger as Director. IfA main headquarters are located at 2680 Woodlawn Drive in Honolulu, Hawaii, , on the University of Hawaii at Mānoa campus. Additional facilities are located at Pukalani,...
  
   – (organization) Institute for Astronomy, the astronomy research division of the University of Hawaii
  University of Hawaii
  The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...
  
  
• IGM – (celestial object) InterGalactic Medium
• IGR – (catalog) Integral Gamma-Ray source, a catalog based on observations by the INTEGRAL
  INTEGRAL
  The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
  
   telescope
• IGY
  International Geophysical Year
  The International Geophysical Year was an international scientific project that lasted from July 1, 1957, to December 31, 1958. It marked the end of a long period during the Cold War when scientific interchange between East and West was seriously interrupted...
  
   – (observing program) International Geophysical Year, the name given to a series of coordinated geophysical and astronomical observation programs performed in 1957 and 1958
• IHW
  International Halley Watch
  Halley's Comet, named after English astronomer Edmund Halley who first demonstrated its periodicity, returns to the vicinity of the Sun and Earth approximately every 76 years. Since comets are believed to be the most primordial objects in the solar system, their study is of great importance to...
  
   – (organization) International Halley Watch, an organization created to coordinate observations of Halley's Comet in 1986
• ILOM – (spacecraft) In-situ Lunar Orientation Measurement, a mission to measure variations in the orientation of the Moon
  Moon
  The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
  
   from the Moon's surface
• IMBH
  Intermediate-mass black hole
  An Intermediate-mass black hole is a black hole whose mass is significantly more than stellar black holes yet far less than supermassive black holes...
  
   – (celestial object) Intermediate Mass Black Hole
• IMF
  Initial mass function
  The initial mass function is an empirical function that describes the mass distribution of a population of stars in terms of their theoretical initial mass...
  
   – (astrophysics terminology) Initial Mass Function, used to describe the relative numbers of stars of different masses that form during star formation
  Star formation
  Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
  
  
• IMO
  International Meteor Organization
  The International Meteor Organization was founded in 1988 and has several hundred members. IMO was created in response to an ever-growing need for international cooperation on amateur meteor work...
  
   – (organization) International Meteor Organization
• IMPACT – (meeting) International Monitoring Programs for Asteroid and Comet Threat
• IMPS – (observing program) IRAS Minor Planet Survey
• INAG – (organization) Institut National d'Astronomie et de Geophysique
• ING
  Isaac Newton Group of Telescopes
  The Isaac Newton Group of Telescopes or ING operates the William Herschel Telescope, Isaac Newton Telescope and Jacobus Kapteyn Telescope optical telescopes for the Science and Technology Facilities Council , the NWO and the IAC...
  
   – (organization) Isaac Newton Group of Telescopes
• INS – (celestial object) Isolated Neutron Star
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
  
• INT
  Isaac Newton Telescope
  The Isaac Newton Telescope or INT is a 2.54 m optical telescope run by the ING at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984....
  
   – (telescope) Isaac Newton Telescope
• INTEGRAL
  INTEGRAL
  The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
  
   – (telescope) INTErnational Gamma-Ray Astrophysics Laboratory, a gamma-ray space telescope
• IoA
  Institute of Astronomy, Cambridge
  The Institute of Astronomy is the largest of the three astronomy departments in the University of Cambridge, and one of the largest astronomy sites in the UK...
  
   – (organization) Institute of Astronomy, an astronomy research department at Cambridge University
• IOTA
  Infrared Optical Telescope Array
  The Infrared Optical Telescope Array began with an agreement in 1988 among five Institutions, the Smithsonian Astrophysical Observatory, Harvard University, the University of Massachusetts, the University of Wyoming, and MIT/Lincoln Laboratory, to build a two-telescope stellar interferometer for...
  
   – (telescope) Infrared Optical Telescope Array
• IOTA – (organization) International Occultation Timing Association, an organization for monitoring occultation
  Occultation
  An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
  
  s
• IPAC – (organization) Infrared Processing & Analysis Center
• IPMO – (celestial object) Isolated Planetary Mass Objects, another name for isolated planemos or sub-brown dwarf
  Sub-brown dwarf
  A sub-brown dwarf is an astronomical object of planetary mass that is not orbiting a star and is not considered to be a brown dwarf because its mass is below the limiting mass for thermonuclear fusion of deuterium ....
  
  s
• IQSY – (observing program) International Quiet Sun Year, the name given to a series of coordinated Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  -related observational programs performed in 1964 and 1965
• IR
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   – (astrophysics terminology) InfraRed
• IRAC – (instrumentation) Infrared Array Camera, a mid-infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   imager on the Spitzer Space Telescope
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
  
• IRAF – (software) Image Reduction and Analisys Facility, a general-purpose professional data-processing package
• IRAIT – (telescope) – International Robotic Antarctic Infrared Telescope
• IRAM – (organization) Institut de Radio Astronomie Millimetrique
• IRAS – (telecope/catalog) InfraRed Astronomical Satellite, an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   space telescope; also used to describe the catalog produced using the telescope's data
• IRCS – (instrumentation) InfraRed Camera and Spectrograph, an instrument on the Subaru Telescope
• IRDC – (celestial object) Infrared Dark Cloud
• IRS – (instrumentation) InfraRed Spectrograph, an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   spectrometer on the Spitzer Space Telescope
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
  
• IRSA – (organization) Infrared Science Archive
• IRTF
  Infrared Telescope Facility
  The NASA Infrared Telescope Facility is a telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawai'i. It was first built to support the Voyager missions and is now the USA national facility for infrared astronomy, providing continued support to...
  
   – (telescope) InfraRed Telescope Facility
• ISAS
  Institute of Space and Astronautical Science
  is a Japanese national research organization of astrophysics using rockets, astronomical satellites and interplanetary probes. It is a division of Japan Aerospace Exploration Agency .- History :...
  
   – (organization) Institute of Space and Astronautical Science
• ISAS – (organization) Institute of Space and Atmospheric Studies, a research unit at the University of Saskatchewan
  University of Saskatchewan
  The University of Saskatchewan is a Canadian public research university, founded in 1907, and located on the east side of the South Saskatchewan River in Saskatoon, Saskatchewan, Canada. An "Act to establish and incorporate a University for the Province of Saskatchewan" was passed by the...
  
  
• ISEE – (spacecraft) International Sun Earth Explorer, a series of spacecraft designed to study the effects of the Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
   on the Earth's space environment and magnetosphere
• ISGRI – (instrumentation) – INTEGRAL Soft Gamma-Ray Imager, an instrument on the INTEGRAL
  INTEGRAL
  The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
  
   satellite
• ISM
  Interstellar medium
  In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
  
   – (celestial object) InterStellar Medium
• ISN – (organization) International Supernovae Network
• ISO
  Infrared Space Observatory
  The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency , in cooperation with ISAS and NASA...
  
   – (telescope) Infrared Space Observatory
• ISPM
  Ulysses probe
  Ulysses is a decommissioned robotic space probe that was designed to study the Sun as a joint venture of NASA and the European Space Agency . The spacecraft was originally named Odysseus, because of its lengthy and indirect trajectory to near Solar distance...
  
   – (spacecraft) International Solar Polar Mission, another name for the Ulysses spacecraft
  Ulysses probe
  Ulysses is a decommissioned robotic space probe that was designed to study the Sun as a joint venture of NASA and the European Space Agency . The spacecraft was originally named Odysseus, because of its lengthy and indirect trajectory to near Solar distance...
  
  
• ISSA – (data) Infrared Sky Survey Atlas, an atlas compiled from Infrared Astronomical Satellite data
• ISTeC – (organization) International Small Telescope Cooperative
• ISY
  International Space Year
  The International Space Year was 1992, the five-hundredth anniversary of 1492, the year of Christopher Columbus's voyage to the New World. First proposed by US Senator Spark Matsunaga, the designation of 1992 as International Space Year was endorsed by 18 national and international space agencies,...
  
   – (observing program/meeting) International Space Year, the name given to a celebration of space exploration as well as a series of coordinated astronomical observations and a series of meetings to plan future astronomy research efforts
• ITA
  Institute of Astronomy, Cambridge
  The Institute of Astronomy is the largest of the three astronomy departments in the University of Cambridge, and one of the largest astronomy sites in the UK...
  
   – (organization) Institute of Theoretical Astronomy, one of three organizations that was combined to form the Institute of Astronomy
  Institute of Astronomy, Cambridge
  The Institute of Astronomy is the largest of the three astronomy departments in the University of Cambridge, and one of the largest astronomy sites in the UK...
  
  
• IUE
  International Ultraviolet Explorer
  The International Ultraviolet Explorer was an astronomical observatory satellite primarily designed to take ultraviolet spectra. The satellite was a collaborative project between NASA, the UK Science Research Council and the European Space Agency...
  
   – (telescope) International Ultraviolet Explorer, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   space telescope
• IUEDAC – (organization) IUE satellite Data Analysis Center
• IWCA – (meeting) International Workshop on Cometary Astronomy

J

• JAC – (publication) Japan Astronomical Circular
• JAC
  Joint Astronomy Centre
  The Joint Astronomy Centre operates British, Canadian and Dutch telescopes at Mauna Kea Observatory, and provides support for other telescopes and public outreach activities...
  
   – (organization) Joint Astronomy Centre, the organization that operates the United Kingdom Infrared Telescope
  United Kingdom Infrared Telescope
  UKIRT, the United Kingdom Infra-Red Telescope, is a 3.8 metre infrared reflecting telescope, the largest dedicated infrared telescope in the world. It is operated by the Joint Astronomy Centre in Hilo and located on Mauna Kea, Hawai'i as part of Mauna Kea Observatory...
  
   and the James Clerk Maxwell Telescope
  James Clerk Maxwell Telescope
  The James Clerk Maxwell Telescope is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum...
  
  
• JAPOA – (organization) Japan Amateur Photoelectric Observers Association
• JAXA
  Japan Aerospace Exploration Agency
  The , or JAXA, is Japan's national aerospace agency. Through the merger of three previously independent organizations, JAXA was formed on October 1, 2003, as an Independent Administrative Institution administered by the Ministry of Education, Culture, Sports, Science and Technology and the...
  
   – (organization) Japan Aerospace eXploration Agency
• JCMT
  James Clerk Maxwell Telescope
  The James Clerk Maxwell Telescope is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum...
  
   – (telescope) James Clerk Maxwell Telescope
• JD – (astrophysics terminology) Julian Date, an alternative time commonly used in astronomy
• JET-X – (telescope) Joint European Telescope for X-ray astronomy
• JGR
  Journal of Geophysical Research
  The Journal of Geophysical Research is a peer-reviewed scientific journal published by the American Geophysical Union 80 times per year. It contains original research on the physical, chemical, and biological processes that contribute to the understanding of the Earth, Sun, and solar system...
  
   – (publication) Journal of Geophysical Research
• JILA – (organization) formerly Joint Institute for Laboratory Astrophysics
• JKT
  Jacobus Kapteyn Telescope
  The Jacobus Kapteyn Telescope or JKT is a 1m optical telescope of the Isaac Newton Group of Telescopes on La Palma in the Canary Islands. It was funded by Netherlands and the United Kingdom and completed in the early 1980s. Planning procceded throughout the 1970s and it came online in 1983-1984...
  
   – (telescope) Jacobus Kapteyn Telescope
• JPL
  Jet Propulsion Laboratory
  Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
  
   – (organization) Jet Propulsion Laboratory, a research center associated with NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
  
• JSGA – (telescope/organization) Japan SpaceGuard Association, a Japanese telescope used to track near-Earth asteroid
  Asteroid
  Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
  
  s and space junk
• JWST
  James Webb Space Telescope
  The James Webb Space Telescope , previously known as Next Generation Space Telescope , is a planned next-generation space telescope, optimized for observations in the infrared. The main technical features are a large and very cold 6.5 meter diameter mirror, an observing position far from Earth,...
  
   – (telescope) James Webb Space Telescope, a planned space telescope that will supersede the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  

K

• KAIT
  Katzman Automatic Imaging Telescope
  The Katzman Automatic Imaging Telescope is an automated telescope used in the search for supernovae.The KAIT is a computer-controlled reflecting telescope with a 76 cm mirror and a CCD camera to take pictures. It is located at the Lick Observatory near San Jose, California.KAIT can take close to...
  
   – (telescope) Katzman Automatic Imaging Telescope
• KAO
  Kuiper Airborne Observatory
  The Gerard P. Kuiper Airborne Observatory was a national facility operated by NASA to support research in infrared astronomy. The observation platform was a highly modified C-141A jet transport aircraft with a range of 6,000 nautical miles , capable of conducting research operations up to 48,000...
  
   – (telescope) Kuiper Airborne Observatory
• KBO – (celestial object) Kuiper Belt Object
• KCAO – (organization) Kumamoto Civil Astronomical Observatory
• KIC – (catalog) Kepler Input Catalog
  Kepler Input Catalog
  The Kepler Input Catalog is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program and Kepler....
  
  , a catalog of stars with potential extrasolar planets to be observed by the Kepler Mission
  Kepler Mission
  The Kepler spacecraft is an American space observatory, the space-based portion of NASA's Kepler Mission to discover Earth-like planets orbiting other stars. The spacecraft is named in honor of the 17th-century German astronomer Johannes Kepler...
  
  
• KPNO
  Kitt Peak National Observatory
  The Kitt Peak National Observatory is a United States astronomical observatory located on 2,096 m Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O'odham Nation, southwest of Tucson...
  
   – (organization) Kitt Peak National Observatory

L

• L – (astrophysics terminology) Lagrange, used to describe Lagrange points
• L – (catalog) Luyten, a catalog of proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
   measurements of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• LAD-C – (instrumentation) Large Area Debris Collector, a canceled program that was to collect and catalog low orbital dust on the International Space Station
  International Space Station
  The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
  
  
• LAEFF – (organization) Laboratorio de Astrofisica Espacial y Fisica Fundamental, a Spanish astronomy research organization
• LAL – (catalog) LALande, a historical catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• LAMOST – (telescope) Large sky Area Multi-Object fiber Spectroscopic Telescope
• LANL
  Los Alamos National Laboratory
  Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
  
   – (organization) Los Alamos National Laboratory
• LASCO – (instrumentation) Large Angle and Spectrometric COronagraph, an instrument on the Solar and Heliospheric Observatory
  Solar and Heliospheric Observatory
  The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
  
  
• Laser
  Laser
  A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
  
   – (instrumentation) Light Amplification by Stimulated Emission of Radiation
• LBN – (catalog) Lynds Bright Nebula, a catalog of bright nebulae
• LBNL
  Lawrence Berkeley National Laboratory
  The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...
  
   – (organization) Lawrence Berkeley National Laboratory
• LBT
  Large Binocular Telescope
  Large Binocular Telescope is an optical telescope for astronomy located on Mount Graham in the Pinaleno Mountains of southeastern Arizona, and is a part of the Mount Graham International Observatory...
  
   – (telescope) Large Binocular Telescope
• LBV
  Luminous blue variable
  Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars named after S Doradus, the brightest star of the Large Magellanic Cloud. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial...
  
   – (celestial object) Luminous Blue Variable, a type of very bright variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  
• LCDM
  Lambda-CDM model
  ΛCDM or Lambda-CDM is an abbreviation for Lambda-Cold Dark Matter, which is also known as the cold dark matter model with dark energy...
  
   – (astrophysics terminology) Lambda Cold Dark Matter, used to describe models for structure formation in the universe that include dark energy
  Dark energy
  In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
  
  
  • also ΛCDM
• LCOGT
  Las Cumbres Observatory Global Telescope
  Las Cumbres Observatory Global Telescope Network is a non-profit private operating foundation directed by the technologist Wayne Rosing. The network's goal is to build a global network of 50 to 70 longitudinally spaced robotic telescopes for scientific and educational use...
  
   network of autonomous robotic telescopes (2m , 1m and 40cm) at 7 sites in both hemispheres
• LCROSS
  Lunar Reconnaissance Orbiter
  The Lunar Precursor Robotic Program is a program of robotic spacecraft missions which NASA will use to prepare for future human spaceflight missions to the Moon. Two LPRP missions, the Lunar Reconnaissance Orbiter and the Lunar Crater Observation and Sensing Satellite , were launched in June 2009...
  
   – (spacecraft) Lunar CRater Observation and Sensing Satellite
• LCRS
  Las Campanas Redshift Survey
  The Las Campanas Redshift Survey is considered the first attempt to map a large area of the universe out to a redshift of z = 0.2. It was begun in 1991 using the Las Campanas telescope in Chile to catalog 26418 separate galaxies. It is considered one of the first surveys to document the so-called...
  
   – (observing program) Las Campanas Redshift Survey
• LDN – (catalog) Lynds Dark Nebula, a catalog of dark nebula
  Dark nebula
  A dark nebula is a type of interstellar cloud that is so dense that it obscures the light from the background emission or reflection nebula or that it blocks out background stars . The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger...
  
  e
• LDS – (catalog) Luyten Double Star
• LEO
  Low Earth orbit
  A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
  
   – (astrophysics terminology) Low Earth Orbit
• LEST – (telescope) Large Earth-based Solar Telescope
• LETGS – (instrumentation) Low Energy Transmission Gratings Spectrometer, an instrument on the Chandra X-Ray Observatory
  Chandra X-ray Observatory
  The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
  
  
  • also LETG
• LF
  Luminosity function
  The luminosity function or luminous efficiency function describes the average visual sensitivity of the human eye to light of different wavelengths. It should not be considered perfectly accurate in every case, but it is a very good representation of visual sensitivity of the human eye and it is...
  
   – (astrophysics terminology) Luminosity Function, used to describe the spatial density of objects such as star cluster
  Star cluster
  Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...
  
  s and galaxies as a function of their luminosity
  Luminosity
  Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
  
  
• LFT – (catalog) Luyten Five-Tenths, a catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s with proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s exceeding 0.5"
• LGA – (instrumentation) Low Gain Antenna
• LGM – (celestial object) Little Green Men, a humorous name applied to pulsar
  Pulsar
  A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
  
  s soon after their discovery
• LHEA – (organization) Laboratory for High Energy Astrophysics
• LHS – (catalog) Luyten Half-Second, a catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s with proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s exceeding 0.5"
• LIC
  Local Interstellar Cloud
  The Local Interstellar Cloud is the interstellar cloud roughly 30 light years across through which the Earth's solar system is currently moving. The Solar System is thought to have entered the Local Interstellar Cloud at some time between 44,000 and 150,000 years ago and is expected to remain...
  
   – (celestial object) Local Interstellar Cloud, the cloud in the interstellar medium
  Interstellar medium
  In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
  
   through which the solar system
  Solar System
  The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
  
   is currently moving
• LIGO
  LIGO
  LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. Cofounded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO is a joint project between scientists at MIT,...
  
   – (telescope) Laser Interferometer Gravitational Wave Observatory, an instrument for detecting gravitational wave
  Gravitational wave
  In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...
  
  s
• LINEAR
  Lincoln Near-Earth Asteroid Research
  The Lincoln Near-Earth Asteroid Research project is a cooperative project between the United States Air Force, NASA, and MIT's Lincoln Laboratory for the systematic discovery and tracking of near-Earth asteroids. LINEAR was responsible for the majority of asteroid detections since 1998 until...
  
   – (observing program) Lincoln Near-Earth Asteroid Research
• LINER – (celestial object) Low Ionization Nuclear Emission Region, a galactic nucleus that is characterized by spectral line
  Spectral line
  A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
  
   emission from weakly ion
  Ion
  An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
  
  ized gas
• LIRG
  Luminous infrared galaxy
  A luminous infrared galaxy , is a galactic body whose defining characteristic is in emitting more than 1011 solar luminosities in the far-infrared part of the electromagnetic spectrum. A more luminous system, emitting more than 1012 solar luminosities in the far-infrared, is called ultraluminous...
  
   – (celestial object) Luminous Infrared Galaxy, a galaxy that is between 10¹¹ and 10¹² solar luminosities in the infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
  
• LISA
  Laser Interferometer Space Antenna
  The Laser Interferometer Space Antenna is a planned space mission to detect and accurately measure gravitational waves from astronomical sources. LISA was originally conceived as a joint effort between the United States space agency NASA and the European Space Agency...
  
   – (telescope) Laser Interferometer Space Antenna, a series of spacecraft that can be used to detect gravitational wave
  Gravitational wave
  In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...
  
  s
• LLAGN
  Active galactic nucleus
  An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
  
   – (celestial object) Low Luminosity Active Galactic Nucleus, an active galactic nucleus
  Active galactic nucleus
  An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
  
   with a low luminosity
  Luminosity
  Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
  
  
• LLNL
  Lawrence Livermore National Laboratory
  The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
  
   – (organization) Lawrence Livermore National Laboratory
• LMC
  Large Magellanic Cloud
  The Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...
  
   – (celestial object) Large Magellanic Cloud, an irregular galaxy
  Irregular galaxy
  An irregular galaxy is a galaxy that does not have a distinct regular shape, like a spiral or an elliptical galaxy. The shape of an irregular galaxy is uncommon – they do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a...
  
   near the Milky Way
  Milky Way
  The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
  
  
• LMS – (celestial object) Lower Main Sequence
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
   star, used to describe the less massive hydrogen-burning main-sequence star
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
  s
• LMXB – (celestial object) Low-Mass X-Ray Binary, an X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
  -luminous binary star system
  Binary star
  A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
  
   in which one of the stars is a neutron star
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
   or black hole
  Black hole
  A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
  
   that is stripping material away from the other star in the system
• LN2
  Liquid nitrogen
  Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
  
   – (instrumentation) Liquid Nitrogen
• LOFAR
  LOFAR
  LOFAR is the Low Frequency Array for radio astronomy, built by the Netherlands astronomical foundation ASTRON and operated by ASTRON's radio observatory....
  
   – (telescope) LOw Frequency ARray, for radio astronomy
• LONEOS – (observing program) Lowell Observatory Near-Earth Object Search
• LOSS – (observing program) Lick Observatory Supernova Search
• LOTIS – (telescope) Livermore Optical Transient Imaging System, a telescope designed to find the optical counterparts of gamma ray burst
  Gamma ray burst
  Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
  
  s
• LOTOSS – (observing program) Lick Observatory and Tenagra Observatory Supernova Searches
• LP – (catalog) Luyten Palomar, a catalog of proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
   measurements of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• LPI
  Lunar and Planetary Institute
  The Lunar and Planetary Institute is a scientific research institute dedicated to study of the solar system, its formation, evolution, and current state. The Institute is part of the Universities Space Research Association and is supported by the Science Mission Directorate of the National...
  
   – (organization) Lunar and Planetary Institute
• LPL
  Lunar and Planetary Laboratory
  The Lunar and Planetary Laboratory is a research center for planetary science located in Tucson, Arizona. It is also a graduate school, constituting the Department of Planetary Sciences at the University of Arizona...
  
   – (organization) Lunar and Planetary Laboratory, the planetary science department of the University of Arizona
  University of Arizona
  The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...
  
  
• LPO – (organization) La Palma Observatory
• LPV
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
   – (celestial object) Long Period Variable, a type of variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
   that changes in brightness slowly over time
• LRG – (celestial object) Luminous Red Galaxy, generally refers to a dataset of galaxies from the Sloan Digital Sky Survey
  Sloan Digital Sky Survey
  The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P...
  
   that were selected on the basis of their red colors
• LRO
  Lunar Reconnaissance Orbiter
  The Lunar Precursor Robotic Program is a program of robotic spacecraft missions which NASA will use to prepare for future human spaceflight missions to the Moon. Two LPRP missions, the Lunar Reconnaissance Orbiter and the Lunar Crater Observation and Sensing Satellite , were launched in June 2009...
  
   – (spacecraft) Lunar Reconnaissance Orbiter
• LSR
  Local standard of rest
  In astronomy, the local standard of rest or LSR follows the mean motion of material in the Milky Way in the neighborhood of the Sun. The path of this material is not precisely circular...
  
   – (astrophysics terminology) Local Standard of Rest, used to describe the frame of reference with a velocity
  Velocity
  In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
  
   equal to the average velocity of all the star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s in the solar neighborhood, including the Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  
• LSST
  Large Synoptic Survey Telescope
  The Large Synoptic Survey Telescope is a planned wide-field "survey" reflecting telescope that will photograph the available sky every three nights. The LSST is currently in its design and development phase and will achieve engineering first light four years after construction starts...
  
   – (telescope) Large Synoptic Survey Telescope
• LST – (astrophysics terminology) Local Sidereal Time, the right ascension
  Right ascension
  Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
  
   that is currently at the zenith
  Zenith
  The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
  
  
• LTE
  Thermodynamic equilibrium
  In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, radiative equilibrium, and chemical equilibrium. The word equilibrium means a state of balance...
  
   – (astrophysics terminology) Local Thermodynamic Equilibrium, refers to a state where variations in temperature, pressure, etc. do not vary on small scales
• LTP – (astrophysics terminology) Lunar Transient Phenomenon, used to describe an observed event (such as a flash of light) on the surface of the Moon
  Moon
  The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
  
  
• LTT – (catalog) Luyten Two-Tenths, a catalog of proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
   measurements for star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s

M

• MARVEL – (project) Multi-object Apache Point Observatory Radial Velocity Exoplanet Large-area Survey, a NASA-funded project to search for exoplanets
• M
  Messier object
  The Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets...
  
   – (catalog) Messier
• M
  Mira variable
  Mira variables , named after the star Mira, are a class of pulsating variable stars characterized by very red colors, pulsation periods longer than 100 days, and light amplitudes greater than one magnitude in infrared and 2.5 magnitude in visual...
  
   – (celestial object) Mira, a class of long period pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after Mira
  Mira
  Mira also known as Omicron Ceti , is a red giant star estimated 200-400 light years away in the constellation Cetus. Mira is a binary star, consisting of the red giant Mira A along with Mira B. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered,...
  
  , the archetype for the class
• MAC – (observing program) Multi instrument Aircraft Campaign, a program to study the cometary dust from the Leonids
  Leonids
  The Leonids is a prolific meteor shower associated with the comet Tempel-Tuttle. The Leonids get their name from the location of their radiant in the constellation Leo: the meteors appear to radiate from that point in the sky. They tend to peak in November.Earth moves through the meteoroid...
  
   meteor shower
  Meteor shower
  A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...
  
  s
• MACHO
  Massive compact halo object
  Massive astrophysical compact halo object, or MACHO, is a general name for any kind of astronomical body that might explain the apparent presence of dark matter in galaxy halos. A MACHO is a body composed of normal baryonic matter, which emits little or no radiation and drifts through interstellar...
  
   – (celestial object/observing program/catalog) MAssive Compact Halo Object, an object in the Milky Way
  Milky Way
  The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
  
  's halo
  Galactic halo
  The term galactic halo is used to denote an extended, roughly spherical component of a galaxy, which extends beyond the main, visible component. It can refer to any of several distinct components which share these properties:* the galactic spheroid...
  
   thought to comprise part of the galaxy's dark matter
  Dark matter
  In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
  
  ; also used to refer to a survey to detect these sources through gravitational lensing and the catalog of sources detected by the survey
• MACS
  Magellanic Catalogue of Stars
  The Magellanic Catalogue of Stars is a catalogue of positions for 243561 stars covering large areas around the Large and Small Magellanic Cloud . The catalogue was compiled by H.-J. Tucholke, K.S. de Boer and W.C. Seitter, who measured the positions on ESO Schmidt plates taken in 1988/91 and refer...
  
   (catalogue) Magellanic Catalogue of Stars
• MAGIC
  MAGIC (telescope)
  MAGIC is a system of two Imaging Atmospheric Cherenkov telescopes situated at the Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, at about 2200 m above sea level...
  
   – (telescope) Major Atmospheric Gamma-ray Imaging Cherenkov telescope
• MAP
  Wilkinson Microwave Anisotropy Probe
  The Wilkinson Microwave Anisotropy Probe — also known as the Microwave Anisotropy Probe , and Explorer 80 — is a spacecraft which measures differences in the temperature of the Big Bang's remnant radiant heat — the Cosmic Microwave Background Radiation — across the full sky. Headed by Professor...
  
   – (telescope) Microwave-background Anisotropy Probe, an older name for the Wilkinson Microwave Anisotropy Probe
  Wilkinson Microwave Anisotropy Probe
  The Wilkinson Microwave Anisotropy Probe — also known as the Microwave Anisotropy Probe , and Explorer 80 — is a spacecraft which measures differences in the temperature of the Big Bang's remnant radiant heat — the Cosmic Microwave Background Radiation — across the full sky. Headed by Professor...
  
  
• MASER
  Astrophysical maser
  An astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum...
  
   – (astrophysics terminology) Microwave Amplification by Stimulated Emission of Radiation, microwave
  Microwave
  Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
  
   emission that is similar to the optical emission from a laser
  Laser
  A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
  
  
• MBA – (celestial object) Main Belt Asteroid
• MBH
  Black hole
  A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
  
   – (celestial object) Massive Black Hole
• MCG
  Morphological Catalogue of Galaxies
  The Morphological Catalogue of Galaxies ' or Morfologiceskij Katalog Galaktik, is a Russian catalogue of 30642 galaxies compiled by Boris Vorontsov-Velyaminov and V. P. Arkhipova. It is based on a close scrutiny of prints of the Palomar Sky Survey plates, and putatively complete to a photographic...
  
   – (catalog) Morphological Catalog of Galaxies
• MCO
  Mars Climate Orbiter
  The Mars Climate Orbiter was a 338 kilogram robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander...
  
   – (spacecraft) Mars Climate Orbiter
• MDS – (observing program) Medium Deep Survey, a survey of high-redshift
  Redshift
  In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
  
   galaxies with the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• MECO
  Magnetospheric eternally collapsing object
  Magnetospheric Eternally Collapsing Objects or MECOs are proposed alternatives to black holes advocated by Darryl Leiter and Stanley Robertson. They are a variant of eternally collapsing objects or ECOs proposed by Abhas Mitra in 1998. Mitra had devised an ostensive proof that black holes cannot...
  
   – (celestial object) Magnetospheric Eternally Collapsing Object, a type of object proposed as an alternative to supermassive black hole
  Supermassive black hole
  A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
  
  s as the central compact source within active galactic nuclei
• MEPAG – (organization) Mars Exploration Program Analysis Group
• MEPCO – (meeting) Meeting of European Planetary and Cometary Observers
• MER
  Mars Exploration Rover
  NASA's Mars Exploration Rover Mission is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars...
  
   – (spacecraft) Mars Exploration Rover
• MGC – (catalog/observing program) Millennium Galaxy Catalogue
• MGS
  Mars Global Surveyor
  The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...
  
   – (spacecraft) Mars Global Surveyor
• MHD
  Magnetohydrodynamics
  Magnetohydrodynamics is an academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water or electrolytes...
  
   – (astrophysics terminology) MagnetoHydroDynamic
• MICO – (software) Multi-year Interactive Computer Almanac, astronomy almanac software created by the United States Naval Observatory
  United States Naval Observatory
  The United States Naval Observatory is one of the oldest scientific agencies in the United States, with a primary mission to produce Positioning, Navigation, and Timing for the U.S. Navy and the U.S. Department of Defense...
  
  
• MIPS – (instrumentation) Multi-band Imaging Photometer, an instrument on the Spitzer Space Telescope
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
  
• MJD – (astrophysics terminology) Modified Julian Date, the Julian date minus 2400000.5
• MLO
  Mount Laguna Observatory
  The Mount Laguna Observatory or MLO is an astronomical observatory operated by the Astronomy Department of San Diego State University...
  
   – (organization)
• MMO – (spacecraft) Mercury Magnetospheric Orbiter, JAXA space probe to Mercury
  Mercury (planet)
  Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
  
  
• MMR – (astrophysics terminology) Mean-Motion Resonance
• MMT – (telescope) Multiple Mirror Telescope
• MNRAS
  Monthly Notices of the Royal Astronomical Society
  Monthly Notices of the Royal Astronomical Society is one of the world's leading scientific journals in astronomy and astrophysics. It has been in continuous existence since 1827 and publishes peer-reviewed letters and papers reporting original research in relevant fields...
  
   – (publication) Monthly Notices of the Royal Astronomical Society
• MO
  Mars Observer
  The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
  
   – (spacecraft) Mars Observer
• MOA
  Microlensing Observations in Astrophysics
  Microlensing Observations in Astrophysics is a collaborative project between researchers in New Zealand and Japan, led by Professor Yasushi Muraki of Nagoya University. They use microlensing to observe dark matter, extra-solar planets, and stellar atmospheres from the Southern Hemisphere...
  
   – (observing program) Microlensing Observations in Astrophysics, a survey searching for gravitational lenses
• MOC – (instrumentation) Mars Observer Camera, an instrument on the Mars Observer
  Mars Observer
  The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
  
  
• MOID
  Minimum orbit intersection distance
  Minimum orbit intersection distance is a measure used in astronomy to assess collision risk between astronomical objects. It is defined as the distance between the closest points of the osculating orbits of the two bodies in question. Of greatest interest is the risk of a collision with Earth;...
  
   – (astrophysics terminology) Minimum Orbit Intersection Distance, the minimum distance between two objects' orbital paths
• MOLA – (instrumentation) Mars Observer Laser Altimeter, an instrument on the Mars Observer
  Mars Observer
  The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
  
   used to study Mars
  Mars
  Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
  
  's topology
  Topology
  Topology is a major area of mathematics concerned with properties that are preserved under continuous deformations of objects, such as deformations that involve stretching, but no tearing or gluing...
  
  
• MOND
  Modified Newtonian dynamics
  In physics, Modified Newtonian dynamics is a hypothesis that proposes a modification of Newton's law of gravity to explain the galaxy rotation problem. When the uniform velocity of rotation of galaxies was first observed, it was unexpected because Newtonian theory of gravity predicts that objects...
  
   – (astrophysics terminology) Modified Newtonian Dynamics
• MONS – (telescope) Measuring Oscillations in Nearby Stars, a Danish space telescope that was proposed and designed but not built
• MOST
  Microvariability and Oscillations of STars telescope
  The Microvariability and Oscillations of STars telescope, better known simply as MOST, is Canada's first and only space telescope. It is also the smallest space telescope in the world...
  
   – (telescope) Microvariability and Oscillations of STars, a space telescope designed to detect oscillations in the atmospheres of stars and extrasolar planetss in orbit around other stars
• MOST
  Molonglo Observatory Synthesis Telescope
  The Molonglo Observatory Synthesis Telescope is a radio telescope operating at 843 MHz. It is operated by the School of Physics of the University of Sydney...
  
   – (telescope) Molonglo Observatory Synthesis Telescope, an Australian radio telescope
  Radio telescope
  A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
  
  
• MOTIF – (telescope) Maui Optical Tracking and Identification Facility
• MOXE – (instrumentation) Monitoring X-ray Experiment, an X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   all-sky monitor designed for the Spectrum-X-Gamma
  Spectrum-X-Gamma
  Spektr-RG is an international high-energy astrophysics observatory, which is being built under the leadership of the Russian Space Research Institute...
  
   satellite
• MPC – (publication) Minor Planet Circulars (also called Minor Planets and Comets)
• MPEC
  Minor Planet Electronic Circular
  The Minor Planet Electronic Circulars are published by the Minor Planet Center. They generally contain positional observations and orbits of unusual minor planets and all comets. Monthly lists of observable unusual objects, observable distant objects, observable comets and the critical list of...
  
   – (publication) Minor Planet Electronic Circular
• MPF
  Mars Pathfinder
  Mars Pathfinder was an American spacecraft that landed a base station with roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight wheeled robotic rover named Sojourner.Launched on December 4, 1996 by NASA aboard a Delta II booster a...
  
   – (spacecraft) Mars PathFinder
• MPL
  Mars Polar Lander
  The Mars Polar Lander, also referred to as the Mars Surveyor '98 Lander, was a 290-kilogram robotic spacecraft lander, launched by NASA on January 3, 1999, to study the soil and climate of Planum Australe, a region near the south pole on Mars, as part of the Mars Surveyor '98 mission...
  
   – (spacecraft) Mars Polar Lander
• MPO – (space craft) Mercury Planetary Orbiter, ESA space craft to Mercury
  Mercury (planet)
  Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
  
  
• MPP – (instrumentation) Multi-Pinned-Phase, CCD technology that reduces dark current
  Dark current (physics)
  In physics and in electronic engineering, dark current is the relatively small electric current that flows through photosensitive devices such as a photomultiplier tube, photodiode, or charge-coupled device even when no photons are entering the device. It is referred to as reverse bias leakage...
  
   noise
• MPCS – (publication) Minor Planet circulars Supplement
• MPS – (observing project) Microlensing Planet Search, a program designed that detect extrasolar planet
  Extrasolar planet
  An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
  
  s using a gravitational lensing technique
  Gravitational lens
  A gravitational lens refers to a distribution of matter between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer...
  
  
• MRO
  Mars Reconnaissance Orbiter
  Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
  
   – (spacecraft) Mars Reconnaissance Orbiter
• MSP
  Pulsar
  A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
  
   – (celestial object) MilliSecond Pulsar
• MSSS – (organization) Maui Space Surveillance Site
• MSX
  Midcourse Space Experiment
  The Midcourse Space Experiment is a Ballistic Missile Defense Organization satellite experiment to map bright infrared sources in space...
  
   – (telescope) Midcourse Space EXperiment, an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   space telescope
• MSSSO – (organization) Mount Stromlo and Siding Spring Observatories
• MUNICS – (observing program) MUnich Near-Infrared Cluster Survey
• MUSES – (spacecraft) MU Space Engineering Spacecraft, used to describe a Japanese science-related spacecraft launched in a Mu rocket
  Mu (rocket)
  The Mu, also known as M, was a series of Japanese solid-fuelled carrier rockets, which were launched from Uchinoura between 1966 and 2006...
  
  
• MUSTANG
  MUSTANG (camera)
  MUSTANG or the Multiplexed SQUID TES Array at Ninety GHz is a focal plane array bolometer camera built for the Green Bank Telescope . In September of 2006 it became the first instrument to use the GBT at 90 GHz...
  
   – (instrumentation) Multiplexed SQUID TES Array at Ninety GHz, A bolometer camera on the Green Bank Telescope
  Green Bank Telescope
  The Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...
  
  .
• MW
  Milky Way
  The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
  
   – (celestial object) Milky Way
• MWD – (celestial object) Magnetic White Dwarf
• MXRB – (celestial object) Massive X-Ray Binary, an X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
  -luminous binary system consisting of a compact star
  Compact star
  In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
  
   and a very massive star
• MYSO – (celestial object) Massive Young Stellar Object

N

• N
  Nova
  A nova is a cataclysmic nuclear explosion in a star caused by the accretion of hydrogen on to the surface of a white dwarf star, which ignites and starts nuclear fusion in a runaway manner...
  
   – (celestial object) Nova
• NACA – (organization) National Advisory Committee on Aeronautics, the older name for NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
  
• NAMN
  North American Meteor Network
  The North American Meteor Network was established in June 1995 as an electronic network of people using the Internet to share an interest in meteors...
  
   – (organization) North American Meteor Network
• NAOJ
  National Astronomical Observatory of Japan
  The is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations - the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude...
  
   – (organization) National Astronomical Observatory of Japan
• NAS – (organization) Norsk Astronomisk Selskap, the Norwegian name for the Norwegian Astronomical Society
• NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
   – (organization) National Aeronautics and Space Administration
• NASDA – (organization) NAtional Space Development Agency
• NBS
  National Institute of Standards and Technology
  The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
  
   – (organization) National Bureau of Standards, an older name for the National Institute of Standards and Technology
  National Institute of Standards and Technology
  The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
  
  
• NCT – (telescope) Nuclear Compton Telescope – a balloon-borne soft gamma-ray (0.2-15 MeV) telescope.
• NEAP
  Near Earth Asteroid Prospector
  The Near Earth Asteroid Prospector, or NEAP, was a concept for a small innovative commercial spacecraft mission by the private company SpaceDev. The goal was to fly NEAP to a targeted near Earth asteroid residing beyond the Earth's orbit, successfully land one or more scientific instruments on the...
  
   – (spacecraft) Near Earth Asteroid Prospector, a space probe used to study a near-Earth asteroid
• NEAR – (spacecraft) Near Earth Asteroid Rendezvous, a space probe used to study a near-Earth asteroid
• NEAT – (observing program) Near-Earth Asteroid Tracking
• NED
  NASA/IPAC Extragalactic Database
  The NASA/IPAC Extragalactic Database is an on-line astronomical database for astronomers that collates and cross-correlates astronomical information on extragalactic objects...
  
   – (software) NASA/IPAC Extragalactic Database
• NEO – (celestial object) Near-Earth Object
  • also NEA – (celestial object) Near-Earth Asteroid
• NEMP – (celestial object) Nitrogen-Enhanced Metal-Poor star, a type of Carbon star
  Carbon star
  A carbon star is a late-type star similar to a red giant whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds,...
  
   with high amounts of nitrogen
• NEODyS
  NEODyS
  NEODyS is an Italian and Spanish service that provides information on Near Earth Objects with a convenient Web-based interface. It is based on a continually and automatically maintained database of near earth asteroid orbits. This site provides a number of services to the NEO community...
  
   – (organization) Near Earth Objects Dynamic Site, an Italian web-based service that provides information on near-Earth asteroids
• NEOIC – (organization) Near Earth Object Information Center, a United Kingdom organization that provides information on near-Earth asteroids
• NESS – (telescope) Near Earth Space Surveillance, a telescope for observing near-Earth asteroids
• NESSI – (organization) Near Earth Space Surveillance Initiative, a collaboration planning to use a ground-based telescope to observe near-Earth asteroids
• NGC
  New General Catalogue
  The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
  
   – (catalog) New General Catalog
• NGST
  James Webb Space Telescope
  The James Webb Space Telescope , previously known as Next Generation Space Telescope , is a planned next-generation space telescope, optimized for observations in the infrared. The main technical features are a large and very cold 6.5 meter diameter mirror, an observing position far from Earth,...
  
   – (telescope) Next Generation Space Telescope, an older name for the James Webb Space Telescope
  James Webb Space Telescope
  The James Webb Space Telescope , previously known as Next Generation Space Telescope , is a planned next-generation space telescope, optimized for observations in the infrared. The main technical features are a large and very cold 6.5 meter diameter mirror, an observing position far from Earth,...
  
  
• NHICAT – (catalog) Northern HIPASS CATalog, the northern extension of the HIPASS
  HIPASS
  The HI Parkes All Sky Survey was an astronomical survey for neutral atomic hydrogen . Data was taken between 1997 and 2002 using the Parkes Observatory. HIPASS covered 71% of the sky and identified 5317 sources emitting HI's signature wavelength...
  
   catalogue
• NICMOS
  Near Infrared Camera and Multi-Object Spectrometer
  The Near Infrared Camera and Multi-Object Spectrometer is a scientific instrument for infrared astronomy, installed on the Hubble Space Telescope , operating from 1997 to 1999, and from 2002 to 2008...
  
   – (instrumentation) Near Infrared Camera / Multi Object Spectrometer, an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   instrument on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• NIMS – (instrumentation) Near-Infrared Mapping Spectrometer, an instrument on the Galileo spacecraft
  Galileo spacecraft
  Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
  
  
• NIR
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   – (astrophysics terminology) Near-InfraRed
• NIST
  National Institute of Standards and Technology
  The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
  
   – (organization) National Institute of Standards and Technology
• NLTE
  Non-equilibrium thermodynamics
  Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not in thermodynamic equilibrium. Most systems found in nature are not in thermodynamic equilibrium; for they are changing or can be triggered to change over time, and are continuously and discontinuously...
  
   – (astrophysics terminology) Non-Local Thermodynamic Equilibrium, used to describe situations where the temperature, pressure, etc. of a system are not in equilibrium
• NLTT – (catalog) New Luyten Two-Tenths, a catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s with high proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s
• NOAA
  National Oceanic and Atmospheric Administration
  The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
  
   – (organization) National Oceanic and Atmospheric Administration
• NOAO – (organization) National Optical Astronomy Observatories
• NODO
  NASA Orbital Debris Observatory
  NASA Orbital Debris Observatory or NODO was an observatory that hosted NASA-LMT, a 3 meter diameter aperture liquid metal telescope and astronomical survey funded and operated by NASA from 1995 to 2002 in New Mexico, USA. It was a zenith or transit telescope pointed straight up, that used 20...
  
   – (telescope) NASA Orbital Debris Observatory, a now-defunct telescope used to observe space junk and other objects
• NOT – (telescope) NOrdic Telescope
• NPS
  North polar sequence
  The North polar sequence is a group of 96 stars that was used to define stellar magnitudes and colors. The cluster of stars lies within two degrees of the Northern Celestial pole, which makes them visible to everyone on the northern hemisphere....
  
   – (celestial object) North Polar Sequence, a series of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s near the North Celestial Pole once used as standards for measuring magnitudes
  Apparent magnitude
  The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
  
  
• NRAO
  National Radio Astronomy Observatory
  The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...
  
   – (organization) National Radio Astronomy Observatory
• NRL – (organization) Naval Research Laboratory
• NS
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
   – (celestial object) Neutron Star
• NSF
  National Science Foundation
  The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
  
   – (organization) National Science Foundation
• NSO
  National Solar Observatory
  The mission of the National Solar Observatory is to advance knowledge of the Sun, both as an astronomical object and as the dominant external influence on Earth, by providing forefront observational opportunities to the research community...
  
   – (organization) National Solar Observatory
• NSSDC
  National Space Science Data Center
  The National Space Science Data Center serves as the permanent archive for NASA space science mission data. "Space science" pertains to astronomy and astrophysics, solar and space plasma physics, and planetary and lunar science...
  
   – (organization) National Space Science Data Center
• NSV – (catalog) New Suspected Variable, a catalog of variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s
• NT – (astrophysics terminology) Non-Thermal, used to describe radiation that is not related to the emission source's temperature (such as synchrotron
  Synchrotron
  A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronised with the travelling particle beam. The proton synchrotron was originally conceived by Sir Marcus Oliphant...
  
   radiation)
• NTT
  New Technology Telescope
  The New Technology Telescope or NTT is an Alt-Az, 3.58-metre Richey-Chretien telescope part of the European Southern Observatory and began operations in 1989. It is located in Chile at the La Silla Observatory and was an early pioneer on the use of active optics...
  
   – (telescope) New Technology Telescope, a telescope operated by the European Southern Observatory
  European Southern Observatory
  The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
  
  

O

• OAO – (observatory) Okayama Astrophysical Observatory, in Japan
• OAO
  Orbiting Astronomical Observatory
  The Orbiting Astronomical Observatory satellites were a series of four American space observatories launched by NASA between 1966 and 1972, which provided the first high-quality observations of many objects in ultraviolet light...
  
   – (telescope) Orbiting Astronomical Observatory, a series of satellites with astronomical instruments that operated in the 1970s
• OC
  Open cluster
  An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
  
   – (celestial object) Open Cluster, a cluster of stars
• OCA – (organization) Observatoire de la Côte d'Azur
• OCO – (celestial object) Oort Cloud Object, an object (usually a comet
  Comet
  A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
  
  ) in the Oort cloud
  Oort cloud
  The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
  
  
• OGLE
  Optical Gravitational Lensing Experiment
  The Optical Gravitational Lensing Experiment or OGLE is a Polish astronomical project based at the University of Warsaw that is chiefly concerned with discovering dark matter using the microlensing technique. Since the project began in 1992, it has discovered several extrasolar planets as a side...
  
   – (observing program/catalog) Optical Gravitational Lensing Experiment, an observing program to survey the sky for microlensing events
  Gravitational lens
  A gravitational lens refers to a distribution of matter between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer...
  
  ; also refers to the catalog of sources produced by the project
  • BLG – (catalog) BuLGe, used to designate a source detected in the direction of the bulge of the Milky Way
    Milky Way
    The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
    
    
  • TR – (catalog) TRansit, used to designate a potential observation of a microlensing event
    Gravitational lens
    A gravitational lens refers to a distribution of matter between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer...
    
     caused by a transiting star
• OPAG – (organization) Outer Planets Assessment Group, a group established by NASA that provides advice on solar system
  Solar System
  The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
  
   exploration
• ORFEUS – (telescope) Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   space telescope that could be released and later retrieved by the Space Shuttle
  Space Shuttle
  The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
  
  
• OSSE – (instrumentation) Oriented Scintillation Spectrometer Experiment, an instrument on the Compton Gamma Ray Observatory
  Compton Gamma Ray Observatory
  The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
  
  
• OTA – (instrumentation) Optical Telescope Assembly, used to describe the optics of the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• OVV
  OVV quasar
  An optically violent variable quasar is a type of highly variable quasar. It is a subtype of blazar that consists of a few rare, bright radio galaxies, whose visible light output can change by 50% in a day. They are similar in appearance to BL Lacs but generally have a stronger broad emission...
  
   – (celestial object) An Optically Violent Variable quasar.
• OWL – (telescope) Orbiting Wide-angle Light-collectors, two satellites that will work together to observe cosmic rays hitting the Earth's atmosphere
• OSS
  Ohio Sky Survey
  The Ohio Sky Survey was an astronomical survey of extragalactic radio sources. Data were taken between 1965 and 1971 using the Big Ear radio telescope at the Ohio State University Radio Observatory , also known as the "Big Ear Radio Observatory "....
  
   Ohio Sky Survey
• OWL
  Overwhelmingly Large Telescope
  The Overwhelmingly Large Telescope is a conceptual design by the European Southern Observatory organization for an extremely large telescope, which was intended to have a single aperture of 100 meters in diameter...
  
   – (telescope) OverWhelmingly Large Telescope, a proposed telescope with a primary mirror with a width of 100 m

P

• P60 – (telescope) Palomar
  Palomar Observatory
  Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
  
   60-inch telescope
• PA – (astrophysics terminology) Position Angle
• PAH
  Polycyclic aromatic hydrocarbon
  Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...
  
   – (astrophysics terminology) Polycyclic Aromatic Hydrocarbon
• PAMELA – (telescope) Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, a space telescope used to study cosmic ray
  Cosmic ray
  Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
  
  s
• Pan-STARRS
  Pan-STARRS
  The Panoramic Survey Telescope and Rapid Response System is a planned array of astronomical cameras and telescopes and computing facility that will survey the sky on a continual basis, including accurate astrometry and photometry of detected objects...
  
   – (telescope) Panoramic Survey Telescope And Rapid Response System
• PASJ – (publication) Publications of the Astronomical Society of Japan
• PASP
  Publications of the Astronomical Society of the Pacific
  Publications of the Astronomical Society of the Pacific is a monthly scientific journal which publishes astronomy research and review papers, instrumentation papers and dissertation summaries....
  
   – (publication) Publications of the Astronomical Society of the Pacific
• PCA – (instrumentation) Proportional Counter Array, an X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   detector on the Rossi X-ray Timing Explorer
  Rossi X-ray Timing Explorer
  The Rossi X-ray Timing Explorer is a satellite that observes the time structure of astronomical X-ray sources. The RXTE has three instruments—the Proportional Counter Array, the High-Energy X-ray Timing Experiment , and one instrument called the All Sky Monitor...
  
  
• PCAS
  Planet-Crossing Asteroid Survey
  The Palomar Planet Crossing Asteroid Survey was initiated by Eleanor F. Helin and Eugene M. Shoemaker in 1973. This program is responsible for the discovery of several thousand asteroids of all types including a large number of Near-Earth Asteroids , over 200 high inclination objects, other rare...
  
   – (observing program) Planet-Crossing Asteroid Survey
• PDBI
  Plateau de Bure Interferometer
  The Plateau de Bure Interferometer is a six-antenna interferometer on the Plateau de Bure in the French Alps, operated by the Institut de radioastronomie millimétrique....
  
   – (telescope) Plateau de Bure Interferometer, a radio telescope
• PDR
  Photodissociation region
  Photodissociation regions are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat...
  
   – a photodissociation region or photon-dominated region (both terms are used synonymously); a region in the neutral ISM
  Interstellar medium
  In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
  
   in which far-ultraviolet photons dominate the heating and chemistry
• PEP – (instrumentation) PhotoElectric Photometry, used to describe an observing technique using photometer
  Photometer
  In its widest sense, a photometer is an instrument for measuring light intensity or optical properties of solutions or surfaces. Photometers are used to measure:*Illuminance*Irradiance*Light absorption*Scattering of light*Reflection of light*Fluorescence...
  
  s
• PEPE – (instrumentation) Plasma Experiment for Planetary Exploration, an instrument on Deep Space 1
  Deep Space 1
  Deep Space 1 is a spacecraft of the NASA New Millennium Program dedicated to testing a payload of advanced, high risk technologies....
  
  
• PHA – (celestial object) Potentially Hazardous Asteroid
• PI – (person) Principal Investigator, the person who leads a scientific project
• PK – (catalog) Perek-Kohoutek, a catalog of planetary nebula
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
  e
• Planemo – (celestial object) Planetary Mass Object
• PLANET
  Probing Lensing Anomalies Network
  The Probing Lensing Anomalies NETwork collaboration coordinates a network of telescopes to rapidly sample photometric measurements of the magnification of stars in the galactic bulge undergoing gravitational microlensing by intervening foreground stars...
  
   – (observing program) Probing Lensing Anomalies NETwork, a program to search for microlensing events
  Gravitational lens
  A gravitational lens refers to a distribution of matter between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer...
  
  
• PLS – (observing program) Palomar-Leiden Survey, a program to search for asteroid
  Asteroid
  Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
  
  s
• PMPS – (observing program) Parkes Multibeam Pulsar Survey
• PMS – (celestial object) Pre–Main Sequence, used to describe young star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s that are still in the process of formation
  • also pre-MS
• PMT – (instrumentation) PhotoMultiplier Tube
• P-L
  P-L
  In asteroid naming, the designation P–L stands for Palomar–Leiden, named after Palomar Observatory and Leiden Observatory, the observatories at which asteroid searchers Tom Gehrels of the University of Arizona, Ingrid van Houten-Groeneveld and Ingrid's husband Cornelis Johannes van Houten of the...
  
   – a set of asteroid discoveries in the 1960s
• PN
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
   – (celestial object) Planetary Nebula
  • also PNe (plural form of Planetary Nebula)
• PNG – (catalog) Galactic Planetary Nebula
• PNLF
  Planetary nebula luminosity function
  Planetary nebula luminosity function is a secondary distance indicator used in astronomy. It makes use of the [O III] λ5007 forbidden line found in all planetary nebula which are members of the old stellar populations ....
  
   – (astrophysics terminology) Planetary Nebula Luminosity Function, used to describe the density of planetary nebulae as a function of their luminosity
  Luminosity
  Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
  
  
• PNN – (celestial object) Planetary Nebula Nucleus, the central star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
   in a planetary nebula
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
  
• PNNV – (celestial object) Planetary Nebula Nucleus Variable, a variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
   in the center of a planetary nebula
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
  
• POSS – (observing program) Palomar Observatory Sky Survey
• PPARC
  Particle Physics and Astronomy Research Council
  The Particle Physics and Astronomy Research Council was one of a number of Research Councils in the United Kingdom. It directed, coordinated and funded research in particle physics and astronomy for the people of the UK...
  
   – (organization) Particle Physics and Astronomy Research Council, a major government-sponsored science agency in the United Kingdom, merged into the Science and Technology Facilities Council
  Science and Technology Facilities Council
  The Science and Technology Facilities Council is a UK government body that carries out civil research in science and engineering, and funds UK research in areas including particle physics, nuclear physics, space science and astronomy .-History:It was formed in April 2007 as a merger of the Particle...
  
   in 2007
• PPM – (catalog) Positions and Proper Motions, a catalog of the positions and proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• PPN
  Protoplanetary nebula
  A protoplanetary nebula or preplanetary nebula is an astronomical object which is at the short-lived episode during a star's rapid stellar evolution between the late asymptotic giant branch phase and the subsequent planetary nebula phase. A PPN emits strongly in infrared radiation, and is a...
  
   – (celestial object) Proto-Planetary Nebula, an object that has partially evolved from a red giant
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
   to a planetary nebula
  Planetary nebula
  A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
  
  
• PRE – (astrophysics terminology) Photospheric Radius Expansion
• Proplyd
  Protoplanetary disk
  A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
  
   – (celestial object) Protoplanetary Disk
• PSC – (catalog) Point Source Catalog, a catalog of point-like infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   sources detected with the Infrared Astronomy Satellite
• PSF
  Point spread function
  The point spread function describes the response of an imaging system to a point source or point object. A more general term for the PSF is a system's impulse response, the PSF being the impulse response of a focused optical system. The PSF in many contexts can be thought of as the extended blob...
  
   – (instrumentation) Point Spread Function, a function that describes the blurring of a point source that is caused by the optics of the telescope and instrument (as well as other effects)
• PSI
  Planetary Science Institute
  The Planetary Science Institute is a research institute based in Tucson, Arizona, focusing on planetary science.Founded in 1972 on a non-profit basis, it is involved in many NASA missions, the study of Mars, asteroids, comets, interplanetary dust, the formation of the Solar System, extrasolar...
  
   – (organization) Planetary Science Institute
• PSR
  Pulsar
  A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
  
   – (celestial object) Pulsar
• PVO – (spacecraft) Pioneer Venus Orbiter
• PVTEL
  PV Telescopii variable
  PV Telescopii variable is a type of variable star that is established in the General Catalogue of Variable Stars with the acronym PVTEL. This class of variables are defined as "helium supergiant Bp stars with weak hydrogen lines and enhanced lines of He and C"...
  
   – (celestial object) PV TELescopii, a class of pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after PV Telescopii
  PV Telescopii
  PV Telescopii is a class B-type supergiant in the constelation Telescopium. It is also the prototype of variable stars called PV Telescopii variables. These are blue supergiants with weak Hydrogen lines and enhanced Helium and Carbon lines. Their variable periods are from a few hours to a few...
  
  , the archetype for the class
• PWD – (celestial object) Pre-White Dwarf, a star that no longer creates energy through fusion that will eventually evolve into a white dwarf
  White dwarf
  A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
  
  
• PWN
  Pulsar wind nebula
  A pulsar wind nebula is a nebula powered by the pulsar wind of a pulsar. At the early stages of their evolution, pulsar wind nebulae are often found inside the shells of supernova remnants...
  
   – (celestial object) Pulsar Wind Nebula
• PZT – (telescope) Photographic Zenith Tube, a general name for any telescope designed to observe objects passing at the zenith
  Zenith
  The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
  
  

Q

• QBO
  Quasi-biennial oscillation
  The quasi-biennial oscillation is a quasi-periodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at...
  
   – (astrophysics terminology) Quasi-Biennial Oscillation, a type of season variation in the Earth's atmosphere
• QE – (instrumentation) Quantum Efficiency, used to describe the sensitivity of CCDs
• QPO
  Quasi-periodic oscillations
  In X-ray astronomy, quasi-periodic oscillation is the manner in which the X-ray light from an astronomical object flickers about certain frequencies...
  
   – (astrophysics terminology) Quasi-Periodic Oscillation
• QSO
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
   – (celestial object) Quasi-Stellar Object
• Quasar
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
   – (celestial object) QUASi-stellAR radio source

R

• RAPTOR – Rapid Telescopes for Optical Response project
• RA
  Right ascension
  Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
  
   – (astrophysics terminology) Right Ascension
• RAFGL – See AFGL.
• RAMBO – (celestial object) An association of brown dwarf
  Brown dwarf
  Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
  
  s or white dwarf
  White dwarf
  A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
  
  s form a dark cluster.
• RAS
  Royal Astronomical Society
  The Royal Astronomical Society is a learned society that began as the Astronomical Society of London in 1820 to support astronomical research . It became the Royal Astronomical Society in 1831 on receiving its Royal Charter from William IV...
  
   – (organization) Royal Astronomical Society
• RASC
  Royal Astronomical Society of Canada
  The Royal Astronomical Society of Canada is a national, non-profit, charitable organization devoted to the advancement of astronomy and related sciences. At present, there are 29 local branches of the Society, called centres, located in towns and cities across the country from St. John's,...
  
   – (organization) Royal Astronomical Society of Canada
• RASS – (observing program/catalog) ROSAT All-Sky Survey, used as both a name for a survey with ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   and the catalogs produced from the survey
• RC
  Red clump
  The red clump is a feature in the Hertzsprung-Russell diagram of stars. The red clump is considered the metal-rich counterpart to the horizontal branch. Stars in this part of the Hertzsprung-Russell diagram are sometimes called clump giants...
  
   – (celestial object) Red Clump, used to describe a type of metal-rich
  Metallicity
  In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
  
   red giant
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
   star
  • also RCG – Red Clump Giant
• RC – (catalog) Reference Catalogue, a catalog of nearby galaxies
  • RC2 – Reference Catalogue, 2nd edition
  • RC3 – Reference Catalogue, 3rd edition
• RC – (organization/telescope) Ritchey Chretien, a manufacturer of amateur and professional telescope equipment; also refers to the telescopes themselves
• RCB
  R Coronae Borealis variable
  A R Coronae Borealis variable is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation , and one irregular unpredictably sudden fading by 1 to 9 magnitudes...
  
   – (celestial object) R Coronae Borealis, a class of eruptive variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after R Coronae Borealis
  R Coronae Borealis
  R Coronae Borealis is a yellow supergiant star, and is the prototype of the RCB class of variable stars, which fade by several magnitudes at irregular intervals...
  
  , the archetype for the class
• RDI – (astrophysics terminology) Radiation Driven Implosion
• RECONS – (organization) Research Consortium on Nearby Stars, a survey of nearby stars
• RGB – (celestial object) Red-Giant Branch, used to describe a star that is evolving from a main-sequence star
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
   into a red giant
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
  
• RGO – (organization) Royal Greenwich Observatory
• RLOF – (astrophysics terminology) Roche Lobe Overflow, used to describe the result of when an object in a binary system is larger than its roche lobe
  Roche lobe
  The Roche lobe is the region of space around a star in a binary system within which orbiting material is gravitationally bound to that star. If the star expands past its Roche lobe, then the material can escape the gravitational pull of the star. If the star is in a binary system then the material...
  
   (i.e. when an object in a binary system expands to a radius where tidal forces become stronger than gravitational forces)
• RLQ – (celestial object) Radio Loud Quasar
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
  , a quasar
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
   that produces strong radio emission
• RNGC – (catalog) Revised New General Catalog
• RORF – (astrophysics terminology) Radio/Optical Reference Frame, an inertial reference frame based on extragalactic radio sources
• ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
   – (telescope) ROentgen SATellite, an X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   space telescope
• ROTSE
  Robotic Optical Transient Search Experiment
  The Robotic Optical Transient Search Experiment is an multi-telescope experiment designed to detect gamma-ray bursts. The experiment currently consists of four telescopes located in Australia, Namibia, Turkey, and at the McDonald observatory near Fort Davis, Texas.The ROTSE project is a...
  
   – (observing program/telescope) Robotic Optical Transient Search Experiment, an observing program for detecting the optical counterparts of gamma ray bursts; also used to describe the telescopes used in this program
• RQQ – (celestial object) Radio Quiet Quasar
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
   a quasar
  Quasar
  A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
  
   that produces weak radio emission
• RRAT
  Rotating radio transient
  Rotating radio transients are sources of short, moderately bright, radio pulses, which were first discovered in 2006. RRATs are thought to be pulsars, i.e. rotating magnetised neutron stars which emit more sporadically and/or with higher pulse-to-pulse variability than the bulk of the known pulsars...
  
   – (celestial object) Rotating Radio Transient, a population of rotating neutron star
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
  s that produce periodic bursts of emission that are separated by intervals of minutes or hours
• RRL
  RR Lyrae variable
  RR Lyrae variables are periodic variable stars, commonly found in globular clusters, and often used as standard candles to measure galactic distances.This type of variable is named after the prototype, the variable star RR Lyrae in the constellation Lyra....
  
   – (celestial object) RR Lyrae, a class of pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after RR Lyrae
  RR Lyrae
  RR Lyrae is a variable star in the Lyra constellation. It is the prototype of the RR Lyrae variable class of stars. It has a period of about 13 hours, and oscillates between apparent magnitudes 7 and 8. Its variable nature was discovered by the Scottish astronomer Williamina Fleming at Harvard...
  
  , the archetype of the class
  • also RR
• RSA – (catalog) Revised Shapley Ames, a catalog of nearby galaxies
• RSA – (organization) Russian Space Agency
• RSAA – (organization) Research School of Astronomy and Astrophysics, part of the Institute of Advanced Studies at the Australian National University
  Australian National University
  The Australian National University is a teaching and research university located in the Australian capital, Canberra.As of 2009, the ANU employs 3,945 administrative staff who teach approximately 10,000 undergraduates, and 7,500 postgraduate students...
  
  
• RSG
  Red supergiant
  Red supergiants are supergiant stars of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive...
  
   – (celestial object) Red Super Giant
• RSN – (celestial object) Radio SuperNova
• RTG
  Radioisotope thermoelectric generator
  A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
  
   – (instrumentation) Radioisotope Thermoelectric Generator, a type of power generator used in spacecraft that travel far from the Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  
• RV
  Radial velocity
  Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
  
   – (astrophysics terminology) Radial Velocity, the velocity along the line of sight
• RX – (catalog) ROSAT X-ray, a catalog of sources detected by ROSAT
  ROSAT
  ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
  
  
• RXTE
  Rossi X-ray Timing Explorer
  The Rossi X-ray Timing Explorer is a satellite that observes the time structure of astronomical X-ray sources. The RXTE has three instruments—the Proportional Counter Array, the High-Energy X-ray Timing Experiment , and one instrument called the All Sky Monitor...
  
   – (telescope) Rossi X-Ray Timing Explorer, a space telescope designed to observe variability in X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   emission

S

• S&T
  Sky & Telescope
  Sky & Telescope is a monthly American magazine covering all aspects of amateur astronomy, including the following:*current events in astronomy and space exploration;*events in the amateur astronomy community;...
  
   – (publication) Sky & Telescope
• SAAO
  South African Astronomical Observatory
  South African Astronomical Observatory is the national center for optical and infrared astronomy in South Africa. It was established in 1972. The observatory is run by the National Research Foundation of South Africa. The facility's function is to conduct research in astronomy and astrophysics...
  
   – (organization) South African Astronomical Observatory
• SALT
  Southern African Large Telescope
  The Southern African Large Telescope is a 66m2 area optical telescope with a nominally 9.2 meter aperture but up to about 11.1m x ~9.8 m diameter aperture, and designed mainly for spectroscopy. It is located close to the town of Sutherland in the semi-desert region of the Karoo, South Africa...
  
   – (telescope) Southern African Large Telescope
• SAO
  Smithsonian Astrophysical Observatory
  The Smithsonian Astrophysical Observatory is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory to form the Harvard-Smithsonian Center for Astrophysics .-History:The SAO was founded in 1890 by...
  
   – (organization/catalog) Smithsonian Astrophysical Observatory, the name of astrophysics research organization associated with Harvard University
  Harvard University
  Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
  
  ; also refers to a catalog of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• SARA – (organization) Society of Amateur Radio Astronomers
• SAS – (software) Science Analysis Software, a software package used for processing data from the XMM-Newton Observatory
• SAT – (telescope) Synthetic Aperture Telescope
• SB – (celestial object) Spectroscopic Binary
  • SB1 – Spectroscopic Binary, single lined spectra
  • SB2 – Spectroscopic Binary, double lined spectra
• SB
  Surface brightness
  The overall brightness of an extended astronomical object such as a galaxy, star cluster, or nebula, can be measured by its total magnitude, integrated magnitude or integrated visual magnitude; a related concept is surface brightness, which specifies the brightness of a standard-sized piece of an...
  
   – (astrophysics terminology) Surface Brightness
• SBIG – (organization/instrumentation) Santa Barbara Instrument Group, the name of both a company that manufactures telescope equipment and the company's products
• SBNC – (organization) Small Bodies Names Committee, an older name for the Committee for Small Body Nomenclature
• SCP
  Supernova Cosmology Project
  The Supernova Cosmology Project is one of two research teams that determined the likelihood of an accelerating universe and therefore a positive Cosmological constant, using data from the redshift of Type Ia supernovae...
  
   – (observing program) Supernova Cosmology Project, a project to measure the expansion of the universe
  Universe
  The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
  
   using supernovae at high redshift
  Redshift
  In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
  
  s
• SCR – (observing program) SuperCOSMOS-RECONS, a survey that measured the proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s of star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• SCT
  Schmidt-Cassegrain telescope
  The Schmidt–Cassegrain is a catadioptric telescope that combines a cassegrain reflector's optical path with a Schmidt corrector plate to make a compact astronomical instrument that uses simple spherical surfaces.-Invention and design:...
  
   – (telescope) Schmidt-Cassegrain Telescope, a general name for a type of compact telescope that uses both lenses and mirrors
• SCUBA – (instrumentation) Submillimetre Common User Bolometer Array, a submillimeter imager formerly at the James Clerk Maxwell Telescope
  James Clerk Maxwell Telescope
  The James Clerk Maxwell Telescope is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum...
  
  
• SCUBA-2 – (instrumentation) Submillimetre Common User Bolometer Array 2, a submillimeter imager that will replace SCUBA
• sd
  Subdwarf star
  A subdwarf star, sometimes denoted by "sd", is luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type...
  
   – (celestial object) subdwarf, used to describe stars fainter than main-sequence star
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
  s with the same colors; often used as a prefix to a star's spectral type
• SDO
  Scattered disc
  The scattered disc is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater...
  
   – (celestial object) Scattered Disk Object, Kuiper Belt objects with highly eccentric
  Orbital eccentricity
  The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
  
  , highly inclined orbit
  Orbit
  In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
  
  s
  • also SKBO – Scattered Kuiper Belt Object
• SDOR – (celestial object) S DORadus, a class of eruptive variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after S Doradus
  S Doradus
  S Doradus is the brightest star in the Large Magellanic Cloud, a satellite of the Milky Way. A hypergiant, it is one of the most luminous stars known , but so far away that it is invisible to the naked eye.This star belongs to its own eponymous S Doradus class of variable stars S Doradus is the...
  
  , the archetype for the class
• SDSS
  Sloan Digital Sky Survey
  The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P...
  
   – (observing program/catalog) Sloan Digital Sky Survey, a large imaging and spectroscopic survey; also used to describe the catalog of sources from the survey
• SDSSp – (catalog) Sloan Digital Sky Survey provisory
• SED
  Spectral Energy Distribution
  A spectral energy distribution is a plot of brightness or flux density versus frequency or wavelength of light. It is used in many branches of astronomy to characterize astronomical sources. For example, in radio astronomy, an SED with a negative spectral index around −0.7 would indicate a...
  
   – (astrophyics terminology) Spectral Energy Distribution
• SEDS
  Students for the Exploration and Development of Space
  Students for the Exploration and Development of Space is an international student organization whose purpose is to promote space exploration and development through educational and engineering projects.-Mission statement:...
  
   – (organization) Students for the Exploration and Development of Space
• SERC
  Science and Engineering Research Council
  The Science and Engineering Research Council used to be the UK agency in charge of publicly funded scientific and engineering research activities including astronomy, biotechnology and biological sciences, space research and particle physics...
  
   – (organization) Science and Engineering Research Council
• SEST – (telescope) Swedish-ESO Submillimetre Telescope
• SETI
  SETI
  The search for extraterrestrial intelligence is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life...
  
   – (observing program) Search for Extra-Terrestrial Intelligence
• SF – (astrophysics terminology) Star Formation
• SFR – (astrophyics terminology) Star Formation Rate
• SGF – (organization) SpaceGuard Foundation, an organization that tracks near-Earth asteroids
• SGR
  Soft gamma repeater
  A soft gamma repeater is an astronomical object which emits large bursts of gamma-rays and X-rays at irregular intervals. It is conjectured that they are a type of magnetar or, alternatively, neutron stars with fossil disks around them....
  
   – (celestial object) Soft Gamma Repeater, a type of neutron star
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
   with strong magnetic fields that produces very large bursts of energy
• SID
  Sudden Ionospheric Disturbance
  A sudden ionospheric disturbance is an abnormally high ionization/plasma density in the D region of the ionosphere caused by a solar flare...
  
   – (astrophysics terminology) Sudden Ionospheric Disturbance, a disturbance in the Earth's ionosphere
  Ionosphere
  The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
  
   caused by the Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  
• SIDC – (organization) Sunspot Index Data Center
• SIM
  Space Interferometry Mission
  The Space Interferometry Mission, or SIM, also known as SIM Lite , was a planned space telescope developed by the U.S. National Aeronautics and Space Administration , in conjunction with contractor Northrop Grumman...
  
   – (telescope) Space Interferometry Mission, a planned optical space telescope that will be used to measure distances to star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s
• SIMBAD
  SIMBAD
  SIMBAD is an astronomical database of objects beyond the Solar System...
  
   – (software) Set of Identifications, Measurements, and Bibliography for Astronomical Data, a website that provides catalog data on astronomical objects
• SINGG – (observing program) Survey of Ionization in Neutral Gas Galaxies, a survey of star formation in nearby galaxies selected by gas rich galaxies using H-alpha and ultraviolet observations
• SINGS – (observing program) Spitzer Infrared Nearby Galaxies Survey
• SIPS – (observing program/catalog) Southern Infrared Proper Motion Survey, a program to identify star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s with high proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s at infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   wavelengths
• SIRTF
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
   – (telescope) Space InfraRed Telescope Facility or Shuttle InfraRed Telescope Facility, older names for the Spitzer Space Telescope
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
  
• SIS – (Instrumentation) Superconductor-Isolator-Superconductor
• SKA
  Square Kilometre Array
  The Square Kilometre Array is a radio telescope in development which will have a total collecting area of approximately one square kilometre. It will operate over a wide range of frequencies and its size will make it 50 times more sensitive than any other radio instrument...
  
   – (telescope) Square Kilometre Array
• SL – (catalog) Shoemaker-Levy, used to refer to the comet
  Comet
  A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
  
  s discovered by Shoemaker and Levy
  David H. Levy
  David H. Levy is a Canadian astronomer and science writer most famous for his co-discovery in 1993 of Comet Shoemaker–Levy 9, which collided with the planet Jupiter in 1994.-Biography:...
  
  , particularly Shoemaker-Levy 9
  Comet Shoemaker-Levy 9
  Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...
  
  
• SL
  Spacelab
  Spacelab was a reusable laboratory used on certain spaceflights flown by the Space Shuttle. The laboratory consisted of multiple components, including a pressurized module, an unpressurized carrier and other related hardware housed in the Shuttle's cargo bay...
  
   – (spacecraft) SpaceLab
• SMA
  Submillimeter Array
  The Submillimeter Array consists of eight diameter radio telescopes arranged as an interferometer for submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing James Clerk...
  
   – (telescope) Submillimeter Array
• SMART
  SMART-1
  SMART-1 was a Swedish-designed European Space Agency satellite that orbited around the Moon. It was launched on September 27, 2003 at 23:14 UTC from the Guiana Space Centre in Kourou, French Guiana. "SMART" stands for Small Missions for Advanced Research in Technology...
  
   – (spacecraft) Small Missions for Advanced Research in Technology
• SMBH
  Supermassive black hole
  A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
  
   – (celestial object) Super Massive Black Hole
• SMC
  Small Magellanic Cloud
  The Small Magellanic Cloud is a dwarf galaxy. It has a diameter of about 7,000 light-years and contains several hundred million stars. It has a total mass of approximately 7 billion times the mass of our Sun....
  
   – (celestial object) Small Magellanic Cloud
• SME
  Solar Mesosphere Explorer
  The Solar Mesosphere Explorer was an United States unmanned spacecraft to investigate the processes that create and destroy ozone in Earth's upper atmosphere. The mesosphere is a layer of the atmosphere extending from the top of the stratosphere to an altitude of about...
  
   – (spacecraft) Solar Mesosphere Explorer, a spacecraft used to study the Earth's ozone layer
  Ozone layer
  The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...
  
  
• SMEX – (spacecraft) SMall EXplorers, the name of a series of small astronomical spacecraft; also used to describe the program to develop the spacecraft
• SMM
  Solar Maximum Mission
  The Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....
  
   – (telescope) Solar Maximum Mission, a solar space telescope
• SN – (instrumentation) Signal-to-Noise, used to describe the ratio between the signal from an object and the noise from the detector that measured the signal
  • also SNR – Signal-to-Nosie Ratio
• SN
  Supernova
  A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
  
   – (celestial object) SuperNova
  • also SNe (plural form of SN)
• SNAP – (telescope) SuperNova Acceleration Probe, proposed space telescope
• SNR
  Supernova remnant
  A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
  
   – (celestial object) SuperNova Remnant
• SNU
  Solar neutrino unit
  Solar neutrino unit is a new unit defined for convenience, which is more suitable for very low event rates.In principle there are two ways of detecting solar neutrinos: radiochemical and real time experiments...
  
   – (astrophysics terminology) Solar Neutrino Units
• SOARD – (software) Steward Observatory Asteroid Relational Database
• SOFIA
  Stratospheric Observatory for Infrared Astronomy
  The Stratospheric Observatory for Infrared Astronomy is a joint project of NASA and the German Aerospace Center to construct and maintain an airborne observatory. NASA awarded the contract for the development of the aircraft, operation of the observatory and management of the American part of the...
  
   – (telescope) Stratospheric Observatory for Infrared Astronomy, an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   telescope currently under construction that will fly inside a modified Boeing 747
  Boeing 747
  The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...
  
   aircraft
• SOHO
  Solar and Heliospheric Observatory
  The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
  
   – (telescope) SOlar and Heliospheric Observatory, a solar space telescope
• SPARTAN – (telescope) Shuttle Pointed Autonomous Research Tool for AstroNomy, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   space telescope that can be released and retrieved by the Space Shuttle
  Space Shuttle
  The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
  
  
• SPIRIT – (instrument) SPace InfraRed Imaging Telescope, an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
   instrument on the Midcourse Space Experiment
  Midcourse Space Experiment
  The Midcourse Space Experiment is a Ballistic Missile Defense Organization satellite experiment to map bright infrared sources in space...
  
   spacecraft
• SPS – (spacecraft) Solar Power Satellite, a general name for proposed satellites that would convert solar power into energy and then beam the energy to the surface of a planet (such as Earth) in the form of microwave
  Microwave
  Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
  
  s
• SPT
  South Pole Telescope
  The South Pole Telescope is a 10 metre diameter telescope located at the Amundsen-Scott South Pole Station, Antarctica. It is a microwave/millimetre-wave telescope that observes in a frequency range between 70 and 300 GHz...
  
   – (telescope) South Pole Telescope
• SQIID – (instrumentation) Simultaneous Quad Infrared Imaging Device
• SQM
  Strange matter
  Strange matter is a particular form of quark matter, usually thought of as a "liquid" of up, down, and strange quarks. It is to be contrasted with nuclear matter, which is a liquid of neutrons and protons , and with non-strange quark matter, which is a quark liquid containing only up and down quarks...
  
   – (celestial object) Strange Quark Matter
• SR
  Special relativity
  Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
  
   – (astrophysics terminology) Special Relativity
• SRON – (organization) Space Research Organization of the Netherlands
• SS – (celestial object) Symbiotic Star, a type of binary star
  Binary star
  A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
  
   system containing a red giant
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
   and a hot dwarf star that generate a cone-shaped nebula
  Nebula
  A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...
  
  
• SSI – (instrumentation) Solid-State Imager, an instrument on the Galileo spacecraft
  Galileo spacecraft
  Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
  
  
• SSI
  Space Studies Institute
  Space Studies Institute is a non-profit organization that was founded in 1977 by the late Princeton University Professor Dr. Gerard K. O'Neill. The stated mission is to "open the energy and material resources of space for human benefit within our lifetime"...
  
   – (organization) Space Studies Institute
• SSP – (instrumentation) – Surface-Science Package, on board the Huygens probe
  Huygens probe
  The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
  
  
• SSS – (observing program) SuperCOSMOS Sky Surveys
• SSSPM – (catalog) SuperCOSMOS Sky Survey Proper Motion
• SST – (telescope) Spectroscopic Survey Telescope
• SST
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
   – (telescope) Spitzer Space Telescope
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
  , a space telescope
• STEPS – (observing program) STEllar Planet Survey
• STIS
  Space Telescope Imaging Spectrograph
  The Space Telescope Imaging Spectrograph is a spectrograph, also with a camera mode, installed on the Hubble Space Telescope. It operated continuously from 1997 until a power supply failure in 2004. After repairs, it began operating again in 2009...
  
   – (instrumentation) Space Telescope Imaging Spectrograph, an instrument on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• STS
  Space Shuttle program
  NASA's Space Shuttle program, officially called Space Transportation System , was the United States government's manned launch vehicle program from 1981 to 2011...
  
   – (vehicle) Shuttle Transport System or Space Transportation System
• STScI
  Space Telescope Science Institute
  The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
  
   – (organization) Space Telescope Science Institute
• STSDAS
  Space Telescope Science Data Analysis System
  The Space Telescope Science Data Analysis System is an IRAF-based suite of astronomical software intended primarily for processing data from the Hubble Space Telescope. STSDAS is produced by Space Telescope Science Institute .-External links:...
  
   – (software) Space Telescope Science Data Analysis System
• SUGRA
  Supergravity
  In theoretical physics, supergravity is a field theory that combines the principles of supersymmetry and general relativity. Together, these imply that, in supergravity, the supersymmetry is a local symmetry...
  
   – (astrophysics terminology) SUperGRAvity
• SUPRIME – (instrumentation) SUbaru PRIME focus CAMera, an instrument on the Subaru Telescope
• SUSI – (telescope) Sydney University Stellar Interferometer, an optical interferometer
  Astronomical interferometer
  An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....
  
  
• SWAN – (instrumentation) Solar Wind ANisotropy, an instrument on SOHO
  Solar and Heliospheric Observatory
  The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
  
  
• SWAS
  Submillimeter Wave Astronomy Satellite
  The Submillimeter Wave Astronomy Satellite was an astronomical observatory launched on December 5, 1998 as part of the Small Explorer program within NASA...
  
   – (telescope) Submillimeter Wave Astronomy Satellite, a submillimeter space telescope
• SWEEPS – (observing program) – Sagittarius Window Eclipsing Extrasolar Planet Search, a survey of a subsection of the plane of the Milky Way
  Milky Way
  The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
  
   performed with the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
  
• SWIRE – (observing program) Spitzer
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
   Wide-area InfraRed Extragalactic survey
• SwRI
  Southwest Research Institute
  Southwest Research Institute , headquartered in San Antonio, Texas, is one of the oldest and largest independent, nonprofit, applied research and development organizations in the United States...
  
   – (organization) Southwest Research Institute
• SXARI
  SX Arietis variable
  SX Arietis variables are a class of variable stars. They are high-temperature analogues of Alpha2 Canum Venaticorum variables and exhibit strong magnetic fields and intense He I and Si III spectral lines. They have brightness fluctuations of approximately 0.1 magnitudes with periods of...
  
   – (celestial object) SX ARIetis, a class of rotating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after SX Arietis, the archetype for the class
• SXPHE
  SX Phoenicis variable
  An SX Phoenicis variable is a type of variable star. These stars exhibit a short period pulsation behavior that varies on time scales of 0.03–0.08 days . They have spectral classifications in the range A2-F5 and vary in magnitude by up to 0.7...
  
   – (celestial object) SX PhoEnicis, a class of pulsating variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after SX Phoenicis, the archetype for the class

T

• TAC – (organization) Time Allocation Committee or Telescope Allocation Committee, a general name for a committee that awards telescope observing time
• TAC – (catalog) Twin Astrograph Catalog
• TAI
  International Atomic Time
  International Atomic Time is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid...
  
   – (astrophysics terminology) International Atomic Time
• TAMS – (astrophysics terminology) Terminal-Age Main Sequence
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
  , used to describe stars at the point in their lifetimes where they have finished burning hydrogen
  Hydrogen
  Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
  
   in their cores
• TAROT – (telescope) Télescope à Action Rapide pour les Objets Transitoires
• TASS – (observing program) The Amateur Sky Survey
• TAU – (spacecraft) Thousand Astronomical Unit, a spacecraft mission proposed in the 1980s that would reach 1000 AU
  Astronomical unit
  An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
  
   in 50 years
• TCB
  Barycentric Coordinate Time
  Barycentric Coordinate Time is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to orbits of planets, asteroids, comets, and interplanetary spacecraft in the Solar system...
  
   – (astrophysics terminology) Barycentric Coordinate Time
• TCG
  Geocentric Coordinate Time
  Geocentric Coordinate Time is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth...
  
   – (astrophysics terminology) Geocentric Coordinate Time
• TDB
  Barycentric Dynamical Time
  Barycentric Dynamical Time is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar system...
  
   – (astrophysics terminology) Barycentric Dynamical Time
• TDRSS
  Tracking and Data Relay Satellite System
  The Tracking and Data Relay Satellite System is a network of American communications satellites and ground stations used by NASA for space communications. The system was designed to replace an existing network of ground stations that had supported all of NASA's manned flight missions...
  
   – (communications network) Tracking and Data Relay Satellite System, an array of satellite
  Satellite
  In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
  
  s used by NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
   to communicate with many spacecraft in low Earth orbit
• TES
  Thermal Emission Spectrometer
  The Thermal Emission Spectrometer is an instrument on board Mars Global Surveyor. TES collects two types of data, hyperspectral thermal infrared data from 6 to 50 micrometers and bolometric visible-NIR measurements...
  
   – (instrumentation) Thermal Emission Spectrometer, a spectrometer
  Spectrometer
  A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
  
   on the Mars Observer
  Mars Observer
  The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
  
  
• TEP – (organization) Transits of Extrasolar Planets
• TGF
  Terrestrial gamma-ray flash
  Terrestrial gamma-ray flashes are bursts of gamma rays in the Earth's atmosphere. TGFs have been recorded to last 0.2 to 3.5 milliseconds, and have energies of up to 20 MeV. They are probably caused by electric fields produced above thunderstorms...
  
   – (celestial object) – Terrestrial gamma-ray flash, gamma ray
  Gamma ray
  Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
  
  s emitted from Earth's lightning
  Lightning
  Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
  
   storms
• THEMIS
  Thermal Emission Imaging System
  The Thermal Emission Imaging System is a camera on board the 2001 Mars Odyssey orbiter. It images Mars in the visible and infrared parts of the electromagnetic spectrum in order to determine the thermal properties of the surface and to refine the distribution of minerals on the surface of Mars as...
  
   – (instrumentation) Thermal Emission Imaging System, a camera on the Mars Odyssey
  2001 Mars Odyssey
  2001 Mars Odyssey is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectrometers and electronic imagers to hunt for evidence of past or...
  
   spacecraft
• TIC – (catalog) Tycho Input Catalog, a predecessor of the Hipparcos Input Catalog
• TIMED
  TIMED
  The TIMED mission was a two year project to study the dynamics of the Mesosphere and Lower Thermosphere portion of the Earth's atmosphere. The mission was launched from Vandenberg Air Force Base in California on December 7, 2001 aboard a Delta II rocket launch vehicle...
  
   – (spacecraft) Thermosphere Ionosphere Mesosphere Energetics and Dynamics
• TIE – (organization) Telescopes In Education
• TLP
  Transient lunar phenomenon
  A transient lunar phenomenon , or lunar transient phenomenon , is a short-lived light, color, or change in appearance on the lunar surface....
  
   – (astrophysics terminology) Transient Lunar Phenomenon, an unexplained flash of light observed from the Moon
  Moon
  The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
  
  
• TMC – (celestial object) Taurus Molecular Cloud
• TMT
  Thirty meter telescope
  The Thirty Metre Telescope is a proposed ground-based large segmented mirror reflecting telescope to be built on Mauna Kea in Hawaii. The telescope is designed for observations from the near-ultraviolet to the mid-infrared . An adaptive optics system would correct for image blur caused by the...
  
   – (telescope) – Thirty Meter Telescope, formerly known as California Extremely Large Telescope
• TN – (person) Telescope Nut, nickname for an amateur telescope maker
• TNO
  Trans-Neptunian object
  A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...
  
   – (celestial object) Trans-Neptunian Object, any object that orbits the Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
   at a distance greater than that of Neptune
  Neptune
  Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
  
  
• TO – (person) Telescope Operator, the technician who assists in operating a telescope during astronomical observations
• TOPS – (meeting) Toward Other Planetary Systems, a series of educational astronomy workshops
• TPF
  Terrestrial Planet Finder
  The Terrestrial Planet Finder was a proposed project by NASA to construct a system of telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled...
  
   – (telescope) Terrestrial Planet Finder, a planned space telescope that will be used to find extrasolar Earth-like planets
  Extrasolar planet
  An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
  
  
• TRACE – Transition Region and Coronal Explorer, a solar space telescope
• TrES – (telescope) Transatlantic Exoplanet Survey
• TT
  Terrestrial Time
  Terrestrial Time is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of the Earth....
  
   – (astrophysics terminology) Terrestrial Time
  • also TDT – Terrestrial Dynamical Time
• TTS
  T Tauri star
  T Tauri stars are a class of variable stars named after their prototype – T Tauri. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines.-Characteristics:...
  
   – (celestial object) T-Tauri Star
• TWA
  TW Hydrae association
  The TW Hydrae association is a group of approximately thirty very young stars located 50 parsecs from Earth that share a common motion and appear to all be roughly the same age, 5-10 million years old...
  
   – (celestial object) TW Hydrae Association
• TYC – (catalog) Tycho, a catalog that was the predecessor of the Hipparcos (HIP) Catalogue
• TZO
  Thorne-Zytkow object
  A Thorne–Żytkow object or TŻO is a hypothetical type of star wherein a red giant or supergiant contains a neutron star at its core. Such objects were hypothesized by Kip Thorne and Anna Żytkow in 1977...
  
   – (celestial object) Thorne-Żytkow Object, the object that forms when a neutron star
  Neutron star
  A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
  
   merges with a red giant
  Red giant
  A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
  
  

U

• UARS
  Upper Atmosphere Research Satellite
  The Upper Atmosphere Research Satellite was a NASA-operated orbital observatory whose mission was to study the Earth’s atmosphere, particularly the protective ozone layer. The satellite was deployed from Space Shuttle Discovery during the STS-48 mission on September 15, 1991...
  
   – (spacecraft) Upper Atmosphere Research Satellite, a satellite used to study the Earth's upper atmosphere
• UCAC – (catalog) USNO CCD Astrometric Catalog
• UESAC – (observing program) Uppsala-ESO Survey of Asteroids and Comets
• UFO
  Unidentified flying object
  A term originally coined by the military, an unidentified flying object is an unusual apparent anomaly in the sky that is not readily identifiable to the observer as any known object...
  
   – (astrophysics terminology) Unidentified Flying Object
• UG
  Dwarf nova
  A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
  
   – (celestial object) U Geminorum, a class of cataclysmic variable stars (also known as dwarf novae) that are named after U Geminorum
  U Geminorum
  U Geminorum , in the constellation Gemini, is an archetypal example of a dwarf nova. The binary star system consists of a white dwarf closely orbiting a red dwarf. Roughly every 100 days it undergoes an outburst that greatly increases its brightness. Discovered by J.R...
  
  , the archetype for the class
  • UGSS
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     – (celestial object) UG SS Cygni, a subclass of UG-type stars
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     named after SS Cygni
    SS Cygni
    SS Cygni is a variable star in the northern constellation Cygnus . It is classified as a dwarf nova, meaning that it undergoes frequent and regular brightness outbursts - every 7 or 8 weeks in the case of this much-observed example. SS Cygni is often classified as a U Geminorum type dwarf nova...
    
    , the archetype for the subclass
  • UGSU
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     – (celestial object) UG SU Ursae Majoris, a subclass of UG-type stars
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     named after SU Ursae Majoris, the archetype for the subclass
  • UGWZ
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     – (celestial object) UG WZ Sagittae, a subclass of UG-type stars
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     named after WZ Sagittae
    WZ Sagittae
    WZ Sagittae is a cataclysmic dwarf nova star system in the Sagitta constellation. it consists of a white dwarf primary being orbited by a low mass companion. The white dwarf is about 0.85 solar masses while the companion is only 0.08 solar masses. This implies that the companion is a spectral...
    
    , the archetype for the subclass
  • UGZ
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     – (celestial object) UG Z Camelopardalis, a subclass of UG-type stars
    Dwarf nova
    A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
    
     named after Z Camelopardalis
    Z Camelopardalis
    Z Camelopardalis is a variable star in the constellation of Camelopardalis. It has an apparent visual magnitude which varies between 10.0 and 14.5. It is the prototype star for the family of Z Camelopardalis variable stars....
    
    , the archetype for the subclass
• UGC
  Uppsala General Catalogue
  The Uppsala General Catalogue of Galaxies is a catalogue of 12921 galaxies visible from the northern hemisphere. It was published the first time in 1973....
  
   – (catalog) Uppsala General Catalogue, a catalog of galaxies
• UIT – (telescope) Ultraviolet Imaging Telescope, an ultraviolet
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   telescope that was operated from the cargo bay of the Space Shuttle
  Space Shuttle
  The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
  
  
• UKIDSS
  UKIRT Infrared Deep Sky Survey
  The UKIRT Infrared Deep Sky Survey or UKIDSS is an astronomical survey conducted using the WFCAM wide field camera on the United Kingdom Infrared Telescope on Mauna Kea in Hawaii...
  
   – (observing program/catalog) UKIRT
  United Kingdom Infrared Telescope
  UKIRT, the United Kingdom Infra-Red Telescope, is a 3.8 metre infrared reflecting telescope, the largest dedicated infrared telescope in the world. It is operated by the Joint Astronomy Centre in Hilo and located on Mauna Kea, Hawai'i as part of Mauna Kea Observatory...
  
   Infrared Deep Sky Survey
• UKIRT
  United Kingdom Infrared Telescope
  UKIRT, the United Kingdom Infra-Red Telescope, is a 3.8 metre infrared reflecting telescope, the largest dedicated infrared telescope in the world. It is operated by the Joint Astronomy Centre in Hilo and located on Mauna Kea, Hawai'i as part of Mauna Kea Observatory...
  
   – (telescope) United Kingdom Infrared Telescope
• UKSA
  UK Space Agency
  The UK Space Agency is a United Kingdom government agency responsible for its civil space programme. It was established on 1 April 2010 to replace the British National Space Centre and took over responsibility for government policy and key budgets for space and represents the UK in all negotiations...
  
   – (organization) UK Space Agency
• UKST
  UK Schmidt Telescope
  The 1.2 metre UK Schmidt Telescope is operated by the Australian Astronomical Observatory , and located adjacent to the 3.9 metre Anglo-Australian Telescope at Siding Spring Observatory, Australia...
  
   – (telescope) United Kingdom Schmidt Telescope
• ULIRG – (celestial object) UltraLuminous InfraRed Galaxy, a galaxy that is brighter than 10¹² solar luminosities in the infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
  
• ULX
  Ultraluminous X-ray source
  An ultra-luminous X-ray source is an astronomical source of X-rays that is less luminous than an active galactic nucleus but is more consistently luminous than any known stellar process , assuming that it radiates isotropically...
  
   – (celestial object) UltraLuminous X-ray source
• UMS – (celestial object) Upper Main Sequence
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
  , used to describe the more massive hydrogen-burning main-sequence star
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
  s
• USAF
  United States Air Force
  The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
  
   – (organization) United States Air Force
• USGS
  United States Geological Survey
  The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
  
   – (organization) United States Geological Survey
• USNO
  United States Naval Observatory
  The United States Naval Observatory is one of the oldest scientific agencies in the United States, with a primary mission to produce Positioning, Navigation, and Timing for the U.S. Navy and the U.S. Department of Defense...
  
   – (organization) United States Naval Observatory
• UT
  Universal Time
  Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...
  
   – (astrophysics terminology) Universal Time
• UTC
  Coordinated Universal Time
  Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
  
   – (astrophysics terminology) Coordinated Universal Time
• UV
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   – (astrophysics terminology) UltraViolet
• UVS – (instrumentation) UltraViolet Spectrometer, the name of instruments on the Voyager
  Voyager program
  The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
  
   and Galileo spacecraft
  Galileo spacecraft
  Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
  
  
• UXOR
  Uxor
  Uxor is the Latin for wife, often abbreviated as ux., and often used in the form "et uxor" or "et ux." to indicate a couple comprising the identified man and his otherwise-unidentified wife...
  
   – (celestial object) UX ORionis objects, a class of variable pre–main sequence stars named after UX Orionis, the archetype for the class

V

• VBO
  Vainu Bappu Observatory
  The Vainu Bappu Observatory, or VBO for short, is an astronomical observatory owned and operated by Indian Institute of Astrophysics. It is located in the Javadi Hills Kavalur, near vaniyambadi of vellore district in the Indian state of Tamil Nadu, 175 km south-east of...
  
   – (organization) Vainu Bappu Observatory, located in India
• VBT – (telescope) Vainu Bappu Telescope, located at Vainu Bappu Observatory
  Vainu Bappu Observatory
  The Vainu Bappu Observatory, or VBO for short, is an astronomical observatory owned and operated by Indian Institute of Astrophysics. It is located in the Javadi Hills Kavalur, near vaniyambadi of vellore district in the Indian state of Tamil Nadu, 175 km south-east of...
  
  
• VCC – (catalog) Virgo Cluster Catalog, a catalog of galaxies in the Virgo Cluster
  Virgo Cluster
  The Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly away in the constellation Virgo. Comprising approximately 1300 member galaxies, the cluster forms the heart of the larger Local Supercluster, of which the Local Group is an outlying member...
  
  
• VdS – (organization) Vereinigung der Sternfreunde, the German amateur astronomers
  Amateur astronomy
  Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
  
   society
• VEEGA – (astrophysics terminology) Venus-Earth-Earth Gravity Assist, used to describe the path taken by the Galileo spacecraft
  Galileo spacecraft
  Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
  
   to reach Jupiter
  Jupiter
  Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
  
  
• VeLLO – (celestial object) Very Low Luminosity Object
• VERITAS
  VERITAS
  VERITAS is a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV - TeV energy range. The telescope design is based on the design of the existing 10m gamma-ray telescope of the Fred Lawrence Whipple Observatory...
  
   – (telescope) Very Energetic Radiation Imaging Telescope Array System, gamma-ray
  Gamma ray
  Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
  
   telescope in Arizona
  Arizona
  Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
  
   sensitive to GeV
  GEV
  GEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
  
  /TeV
  TEV
  TEV may refer to:* TeV, or teraelectronvolt, a measure of energy* Total Enterprise Value, a financial measure* Total Economic Value, an economic measure* Tobacco etch virus, a plant pathogenic virus of the family Potyviridae....
  
   gamma ray
  Gamma ray
  Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
  
  s
• VERA – (telescope) VLBI Exploration of Radio Astrometry, a Japanese radio telescope designed for studying objects in the Milky Way
  Milky Way
  The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
  
  
• VHE – (astrophysics terminology) Very High Energy, used to describe gamma ray
  Gamma ray
  Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
  
  s with high energies
• VIMOS – (instrumentation) VIsible Multi-Object Spectrograph, instrument on the VLT
  Very Large Telescope
  The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
  
  
• VISTA
  VISTA (telescope)
  The VISTA is a reflecting telescope with a 4.1 metre mirror, located at the Paranal Observatory in Chile. It is operated by the European Southern Observatory and saw first light in December 2009...
  
   – (telescope) Visible and Infrared Survey Telescope for Astronomy
• VLA
  Very Large Array
  The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...
  
   – (telescope) Very Large Array, a radio telescope in New Mexico
  New Mexico
  New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
  
   operated by the National Radio Astronomy Observatory
  National Radio Astronomy Observatory
  The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...
  
  
• VLBA
  Very Long Baseline Array
  The Very Long Baseline Array is a system of ten radio telescopes controlled remotely from the Array Operations Center in Socorro, New Mexico by the National Radio Astronomy Observatory. The array works together as the world's largest dedicated, full-time astronomical instrument using the...
  
   – (telescope) Very Long Baseline Array, a radio telescope operated by the National Radio Astronomy Observatory
  National Radio Astronomy Observatory
  The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...
  
   with antennas spread across the United States
• VLBI
  Very Long Baseline Interferometry
  Very Long Baseline Interferometry is a type of astronomical interferometry used in radio astronomy. It allows observations of an object that are made simultaneously by many telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.Data...
  
   – (instrumentation) Very Long Baseline Interferometry, used to describe combining signals from multiple telescopes/radio antennas that are separated by large distances
• VLM – (astrophysics terminology) Very Low Mass, a description for objects (usually star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
  s) that have relatively low masses
• VLT
  Very Large Telescope
  The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
  
   – (telescope) Very Large Telescope, four 8.2 meter telescopes in Chile
  Chile
  Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
  
   that operate either independently as individual telescopes or together as an interferometer
• VMO – (software) The Virtual Meteor Observatory is an activity of the International Meteor Organisation together with the Research and Scientific Support Department of the European Space Agency
  European Space Agency
  The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
  
   to store meteor data from observers all over the world.
• VO
  Virtual Observatory
  Virtual observatory is a collection of interoperating data archives and software tools which utilize the internet to form a scientific research environment in which astronomical research programs can be conducted....
  
   – (software) Virtual Observatory
• VOIR – (spacecraft) Venus Orbiting Imaging Radar, a spacecraft for mapping Venus
  Venus
  Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
  
   that was canceled and then superseded by the Magellan spacecraft
• VRM – (spacecraft) Venus Radar Mapper, an older name for the Magellan spacecraft
• VSOLJ – (organization) Variable Star Observers League in Japan
• VSOP – (organization) VLBI Space Observatory Program, a project to use both satellite
  Satellite
  In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
  
  s and ground-based radio telescope
  Radio telescope
  A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
  
  s as an interferometer
• VST
  VLT Survey Telescope
  The VLT Survey Telescope is the latest telescope to be added to ESO’s Paranal Observatory in the Atacama Desert of northern Chile. It is housed in an enclosure immediately adjacent to the four Very Large Telescope Unit Telescopes on the summit of Cerro Paranal. The VST is a wide-field survey...
  
   – (telescope) VLT Survey Telescope
• VVDS – (observing program) VIMOS-VLT
  Very Large Telescope
  The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
  
   Deep Survey

W

• WD
  White dwarf
  A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
  
   – (celestial object) White Dwarf
• WDM
  Warm dark matter
  Warm dark matter is a hypothesized form of dark matter that has properties intermediate between those of hot dark matter and cold dark matter, causing structure formation to occur bottom-up from above their free-streaming scale, and top-down below their free streaming scale. The most common WDM...
  
   – (astrophysics terminology) Warm Dark Matter, used to describe models for structure formation in the universe that use "hot" particles such as neutrino
  Neutrino
  A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
  
  s as dark matter
  Dark matter
  In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
  
  
• WDS
  Washington Double Star Catalog
  The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for 102,387 pairs of double stars. The catalog also includes multiple stars...
  
   – (catalog) Washington Double Star, a catalog of double star
  Double star
  In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
  
  s
• WEBT
  Whole Earth Blazar Telescope
  The Whole Earth Blazar Telescope is an international consortium of astronomers created in 1997, with the aim to study a particular category of Active Galactic Nuclei called blazars, which are characterized by strong and fast brightness variability, on time scales down to hours or less.This...
  
   – (organization) Whole Earth Blazar Telescope, a network of observers across the Earth who work together to perform continuous observations of blazar
  Blazar
  A blazar is a very compact quasar associated with a presumed supermassive black hole at the center of an active, giant elliptical galaxy...
  
  s
• WET – (organization) Whole Earth Telescope, a network of astronomers spread across the Earth who work together to perform continuous observations of variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s
• WFCAM – (instrumentation) Wide Field Camera, a camera on the United Kingdom Infrared Telescope
  United Kingdom Infrared Telescope
  UKIRT, the United Kingdom Infra-Red Telescope, is a 3.8 metre infrared reflecting telescope, the largest dedicated infrared telescope in the world. It is operated by the Joint Astronomy Centre in Hilo and located on Mauna Kea, Hawai'i as part of Mauna Kea Observatory...
  
  
• WFMOS – (instrumentation) Wide-Field Multi-Object Spectrograph, proposed instrument for the Gemini telescopes
• WFPC
  Wide Field and Planetary Camera
  The Wide Field/Planetary Camera was a camera installed on the Hubble Space Telescope until December 1993. It was one of the instruments on Hubble at launch, but its functionality was severely impaired by the defects of the main mirror optics which afflicted the telescope...
  
   – (instrumentation) Wide Field and Planetary Camera, a camera formerly on the Hubble Space Telescope
  Hubble Space Telescope
  The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
  
   that was replaced with WFPC2
  Wide Field and Planetary Camera 2
  The Wide Field and Planetary Camera 2 is a baby grand piano sized camera built by the Jet Propulsion Laboratory and formerly installed on the Hubble Space Telescope. It was installed by servicing mission 1 in 1993, replacing the telescope's original Wide Field and Planetary Camera...
  
  
• WFPC2
  Wide Field and Planetary Camera 2
  The Wide Field and Planetary Camera 2 is a baby grand piano sized camera built by the Jet Propulsion Laboratory and formerly installed on the Hubble Space Telescope. It was installed by servicing mission 1 in 1993, replacing the telescope's original Wide Field and Planetary Camera...
  
   – (instrumentation) Wide Field and Planetary Camera 2, a camera on the Hubble Space Telescope
• WFC – (instrumentation) Wide-Field Channel, one of the detectors in the Advanced Camera for Surveys
  Advanced Camera for Surveys
  The Advanced Camera for Surveys is a third generation axial instrument aboard the Hubble Space Telescope . The initial design and scientific capabilities of ACS were defined by a team based at Johns Hopkins University. ACS was assembled and tested extensively at Ball Aerospace & Technologies Corp...
  
   on the Hubble Space Telescope
• WGPSN – (organization) Working Group for Planetary System Nomenclature
• WHT
  William Herschel Telescope
  The William Herschel Telescope is a optical/near-infrared reflecting telescope located at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, Spain. The telescope, which is named after William Herschel, is part of the Isaac Newton Group of Telescopes...
  
   – (telescope) William Herschel Telescope
• WIMP – (celestial object) Weakly Interacting Massive Particle, a hypothetical subatomic particle that may comprise most of the dark matter in the universe
• WIRCam – (instrumentation) Wide-field InfraRed Camera, instrument on the Canada-France-Hawaii Telescope
  Canada-France-Hawaii Telescope
  The Canada–France–Hawaii Telescope is located near the summit of Mauna Kea mountain on Hawaii's Big Island at an altitude of 4,204 meters , and is one of the observatories that comprise the Mauna Kea Observatory...
  
  
• WISARD – (software) Web Interface for Searching Archival Research Data
• WISE
  Wide-field Infrared Survey Explorer
  Wide-field Infrared Survey Explorer is a NASA infrared-wavelength astronomical space telescope launched on December 14, 2009, and decommissioned/hibernated on February 17, 2011 when its transmitter was turned off...
  
   – (observing program) Wide-field Infrared Survey Explorer
• WIYN
  WIYN Observatory
  The WIYN Observatory is owned and operated by the WIYN Consortium. Its telescope, a 3.5-meter instrument, is the newest and second largest telescope on Kitt Peak in Arizona...
  
   – (telescope) Wisconsin-Indiana-Yale-NOAO, the name of a telescope at Kitt Peak
  Kitt Peak
  Kitt Peak is a mountain in the U.S. state of Arizona. It is the location of the Kitt Peak National Observatory. The radio telescope at the Observatory is one of ten dishes comprising the Very Long Baseline Array ....
  
   operated by the University of Wisconsin–Madison
  University of Wisconsin–Madison
  The University of Wisconsin–Madison is a public research university located in Madison, Wisconsin, United States. Founded in 1848, UW–Madison is the flagship campus of the University of Wisconsin System. It became a land-grant institution in 1866...
  
  , Indiana University
  Indiana University
  Indiana University is a multi-campus public university system in the state of Indiana, United States. Indiana University has a combined student body of more than 100,000 students, including approximately 42,000 students enrolled at the Indiana University Bloomington campus and approximately 37,000...
  
  , Yale University
  Yale University
  Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...
  
  , and the National Optical Astronomy Observatory
  National Optical Astronomy Observatory
  The National Optical Astronomy Observatory is the United States national observatory for ground based nighttime ultraviolet-optical-infrared astronomy. The National Science Foundation funds NOAO to provide forefront astronomical research facilities for US astronomers...
  
  
• WLM
  Wolf-Lundmark-Melotte
  The Wolf-Lundmark-Melotte galaxy is an irregular galaxy discovered in 1909 by Max Wolf, and is located on the outer edges of the local group. The discovery of the nature of the galaxy was accredited to Knut Lundmark and Philibert Jacques Melotte in 1926. It is in the constellation Cetus.-Star...
  
   – (celestial object) Wolf-Lundmark-Melotte, a nearby dwarf galaxy
  Dwarf galaxy
  A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...
  
   in the constellation
  Constellation
  In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
  
   Cetus
  Cetus
  Cetus is a constellation. Its name refers to Cetus, a sea monster in Greek mythology, although it is often called 'the whale' today. Cetus is located in the region of the sky that contains other water-related constellations such as Aquarius, Pisces, and Eridanus.-Ecliptic:Although Cetus is not...
  
  
• WMAP
  Wilkinson Microwave Anisotropy Probe
  The Wilkinson Microwave Anisotropy Probe — also known as the Microwave Anisotropy Probe , and Explorer 80 — is a spacecraft which measures differences in the temperature of the Big Bang's remnant radiant heat — the Cosmic Microwave Background Radiation — across the full sky. Headed by Professor...
  
   – (telescope) Wilkinson Microwave Anisotrophy Probe, a space telescope used to study the cosmic microwave background radiation
  Cosmic microwave background radiation
  In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
  
  
• WR
  Wolf-Rayet star
  Wolf–Rayet stars are evolved, massive stars , which are losing mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s...
  
   – (celestial object) Wolf-Rayet, a type of hot, luminous star with strong stellar winds
  • WC – (celestial object) Carbon-rich Wolf-Rayet, a Wolf-Rayet star
    Wolf-Rayet star
    Wolf–Rayet stars are evolved, massive stars , which are losing mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s...
    
     with strong carbon
    Carbon
    Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
    
     spectral line
    Spectral line
    A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
    
     emission
  • WN – (celestial object) Nitrogen-rich Wolf-Rayet, a Wolf-Rayet star with strong nitrogen
    Nitrogen
    Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
    
     spectral line emission
    • WNE – (celestial object) Early-type Nitrogen-rich Wolf-Rayet, a WN star without hydrogen
      Hydrogen
      Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
      
       spectral line emission
    • WNL – (celestial object) Late-type Nitrogen-rich Wolf-Rayet, a WN star with hydrogen spectral line emission
  • WO – (celestial object) Oxygen-rich Wolf-Rayet, a Wolf-Rayet star with strong oxygen
    Oxygen
    Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
    
     spectral line emission
• WSRT
  Westerbork Synthesis Radio Telescope
  The Westerbork Synthesis Radio Telescope is an aperture synthesis interferometer near camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands. It consists of a linear array of 14 antennas with a diameter of 25 metres arranged on a 2.7 km East-West line...
  
   – (telescope) an aperture synthesis interferometer that consists of a linear array of 14 antennas
• WTTS – (celestial object) Weak-Line T-Tauri Star, a type of young star
  Star
  A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
  
   with weak spectral line emission

X

• XCS – (observing program) XMM
  XMM-Newton
  The XMM-Newton is an orbiting X-ray observatory launched by ESA in December 1999 on a Ariane 5 rocket...
  
   Cluster Survey
• XIS – (instrumentation) X-ray imaging spectrometer, an instrument on the Suzaku
  ASTRO-E
  Suzaku is a Japanese X-ray astronomy satellite launched on 10 July 2005 aboard the M-V-6 rocket. The project was renamed Suzaku after its successful launch after the mythical Vermilion bird of the South....
  
   space telescope
• XMM
  XMM-Newton
  The XMM-Newton is an orbiting X-ray observatory launched by ESA in December 1999 on a Ariane 5 rocket...
  
   – (telescope) X-ray Multi Mirror, part of the name of the XMM-Newton
  XMM-Newton
  The XMM-Newton is an orbiting X-ray observatory launched by ESA in December 1999 on a Ariane 5 rocket...
  
   X-ray
  X-ray
  X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
  
   space telescope
• XN – (celestial object) X-ray Nova
• XRF – (celestial object) X-Ray Flash

Y

• Ys
  Blue straggler
  Blue stragglers are main sequence stars in open or globular clusters that are more luminous and bluer than stars at the main sequence turn-off point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3...
  
   – (celestial object) Yellow Straggler
• YSG
  Yellow supergiant
  A yellow supergiant is a supergiant star of spectral type F or G. These stars usually have masses between 15 and 20 solar masses. These stars, like any other supergiant,...
  
   – (celestial object) Yellow Super Giant star
• YSO
  Young stellar object
  Young stellar object denotes a star in its early stage of evolution.This class consists of two groups of objects: protostars and pre–main sequence stars. Sometimes they are divided by mass - massive YSO , intermediate mass YSO and brown dwarfs....
  
   – (celestial object) Young Stellar Object

Z

• ZAHB – (celestial object) "Zero-Age" Horizontal Branch
  Horizontal branch
  The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
  
  , a description for horizontal branch
  Horizontal branch
  The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
  
   stars that have just begun burning helium in their cores and hydrogen in a shell around the cores
• ZAMS – (celestial object) Zero Age Main Sequence
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
  , a description for a star that has just become a main-sequence star
  Main sequence
  The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
  
   (i.e. a star that has begun burning hydrogen in its core)
• ZAND – (celestial object) Z ANDromedae, a class of eruptive variable star
  Variable star
  A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
  
  s named after the binary star system
  Binary star
  A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
  
   Z Andromedae
  Z Andromedae
  Z Andromedae is a symbiotic variable star with an hourglass-shaped nebula . It is the prototype for symbiotic variables, which are a subset of cataclysmic variables.-External links:* * * * * *...
  
  , the archetype for the class
  • ZANDE – (celestial object) Z ANDromedae with Eclipses, a subclass of ZAND stars where the stars eclipse each other
• ZEPLIN – (instrumentation) ZonEd Proportional scintillation in LIquid Noble gases, a dark matter detector
• ZHR
  Zenithal Hourly Rate
  In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith...
  
   – (astrophysics terminology) Zenith Hourly Rate, the maximum number of meteor
  METEOR
  METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
  
  s per hour that may be observed during a meteor shower
  Meteor shower
  A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...
  
  

See also

• List of common astronomy symbols
• Modern Constellations
• List of astronomical catalogues

External links

• The Canonical Astronomy Abbreviations/Acronyms List
• Astronomy Acronyms and Astronomy Abbreviations