Deep sky
Encyclopedia
Deep-sky objects are astronomical objects other than individual stars and solar system
objects (such as Sun
, Moon
, planet
s, comet
s, etc.). The classification is used for the most part by amateur astronomers to denote visually observed faint naked eye and telescopic
objects such as star cluster
s, nebula
e and galaxies
.
's 1774 Messier catalog, which included 103 "nebulae" and other faint fuzzy objects he considered a nuisance since they could be mistaken for comets, the objects he was actually searching for. As telescopes improved these faint nebulae would be broken into more descriptive scientific classifications such as interstellar cloud
s, star clusters, and galaxies.
"Deep-sky object", as an astronomical classification for these objects has its origins in the modern field of amateur astronomy. The origin of the term is unknown but it was popularized by Sky & Telescope
magazine's "Deep-Sky Wonders" column, which premiered in their first edition in 1941, created by Leland S. Copeland, written for the majority of its run by Walter Scott Houston
, and currently penned by Sue French. Houston's columns, and later book compilations of those columns, helped popularize the term, each month giving the reader a guided tour of a small part of the sky highlighting well known and lesser known objects for binoculars and small telescopes.
, and since they are invisible to the naked eye, can be hard to find. This has led to increased popularity in GoTo telescopes
that can find DSO’s automatically, and large reflecting telescope
s, such as Dobsonian style telescopes, with wide fields of view well suited for such observing. Observing faint objects need dark skies, so these relatively portable types of telescopes also lend themselves to the majority of amateurs who need to travel outside light polluted
urban locations. To cut down light pollution and enhance contrast observers employ "nebular filters" designed to admit certain wavelength and block others.
There are organized activities associated with DSOs such as the Messier marathon
which occurs at a specific time each year and involve observers trying to spot all 110 Messier objects in one night. Since the Messier catalog objects were discovered with relatively small 18th century telescopes it is a popular list with observers, being well within the grasp of most modern amateur telescopes. A much more demanding test known as the Herschel 400
is designed to tax larger telescopes and experienced amateur astronomers.
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...
objects (such as 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...
, 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...
, planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s, 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, etc.). The classification is used for the most part by amateur astronomers to denote visually observed faint naked eye and telescopic
Optical telescope
An optical telescope is a telescope which is used to gather and focus light mainly from the visible part of the electromagnetic spectrum for directly viewing a magnified image for making a photograph, or collecting data through electronic image sensors....
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, nebula
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...
e and galaxies
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...
.
Origins and classification
Classifying non-stellar astronomical objects began soon after the invention of the telescope. One of the earliest comprehensive list was Charles MessierCharles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
's 1774 Messier catalog, which included 103 "nebulae" and other faint fuzzy objects he considered a nuisance since they could be mistaken for comets, the objects he was actually searching for. As telescopes improved these faint nebulae would be broken into more descriptive scientific classifications such as interstellar cloud
Interstellar cloud
Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it...
s, star clusters, and galaxies.
"Deep-sky object", as an astronomical classification for these objects has its origins in the modern field of amateur astronomy. The origin of the term is unknown but it was popularized by Sky & Telescope
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;...
magazine's "Deep-Sky Wonders" column, which premiered in their first edition in 1941, created by Leland S. Copeland, written for the majority of its run by Walter Scott Houston
Walter Scott Houston
Walter Scott Houston was an American popularizer of amateur astronomy. He wrote the "Deep-Sky Wonders" column in Sky and Telescope magazine from 1946 to 1993.-Biography:...
, and currently penned by Sue French. Houston's columns, and later book compilations of those columns, helped popularize the term, each month giving the reader a guided tour of a small part of the sky highlighting well known and lesser known objects for binoculars and small telescopes.
Observations and activities
There are many amateur astronomical techniques and activities associated with deep-sky objects. Some of these objects are bright enough to find and see in binoculars and small telescopes. But the most fainter objects need the light-gathering power of telescopes with large objectivesObjective (optics)
In an optical instrument, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be single lenses or mirrors, or combinations of several optical elements. They are used in microscopes, telescopes,...
, and since they are invisible to the naked eye, can be hard to find. This has led to increased popularity in GoTo telescopes
GoTo (telescopes)
In amateur astronomy, "GoTo" refers to a type of telescope mount and related software which can automatically point a telescope to astronomical objects that the user selects...
that can find DSO’s automatically, and large reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
s, such as Dobsonian style telescopes, with wide fields of view well suited for such observing. Observing faint objects need dark skies, so these relatively portable types of telescopes also lend themselves to the majority of amateurs who need to travel outside light polluted
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:...
urban locations. To cut down light pollution and enhance contrast observers employ "nebular filters" designed to admit certain wavelength and block others.
There are organized activities associated with DSOs such as the Messier marathon
Messier marathon
A Messier marathon is an attempt, usually organized by amateur astronomers, to find as many Messier objects as possible during one night. The Messier catalogue was compiled by French astronomer Charles Messier during the late 18th century and consists of 110 relatively bright deep sky objects...
which occurs at a specific time each year and involve observers trying to spot all 110 Messier objects in one night. Since the Messier catalog objects were discovered with relatively small 18th century telescopes it is a popular list with observers, being well within the grasp of most modern amateur telescopes. A much more demanding test known as the Herschel 400
Herschel 400 Catalogue
The Herschel 400 catalogue is a subset of William Herschel's original deep sky catalogue of 2,500 deep sky objects, selected by Brenda F. Guzman , Lydel Guzman, Paul Jones, James Morrison, Peggy Taylor and Sara Saey of the Ancient City Astronomy Club in St. Augustine, Florida, USA circa 1980...
is designed to tax larger telescopes and experienced amateur astronomers.
List of deep-sky objects
There are many astronomical object types that come under the description of deep-sky objects. Since the definition is objects that are non-solar system and non-stellar the list includes:- Star clusterStar clusterStar 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- Open clusterOpen clusterAn 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...
s - Globular clusterGlobular clusterA globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
s
- Open cluster
- NebulaNebulaA nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...
e- Bright nebulae
- Emission nebulaEmission nebulaAn emission nebula is a cloud of ionized gas emitting light of various colors. The most common source of ionization is high-energy photons emitted from a nearby hot star...
e - Reflection nebulaReflection nebulaIn Astronomy, reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. The energy from the nearby star, or stars, is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust...
e
- Emission nebula
- Dark nebulaDark nebulaA 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 - Planetary nebulaPlanetary nebulaA 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
- Bright nebulae
- GalaxiesGalaxyA 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...
See also
- Amateur telescope makingAmateur telescope makingAmateur 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...
- Shallow skyShallow skyShallow sky is a term sometimes used by amateur astronomers, as the opposite to deep sky. The shallow sky is space within our solar system, plus our own atmosphere...
- Star cartographyStar cartographyCelestial cartography, uranography or star cartography, is the fringe of astronomy and branch of cartography concerned with mapping stars, galaxies, and other astronomical objects on the celestial sphere...
- Star catalogueStar catalogueA star catalogue, or star catalog, is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some...
- Star hoppingStar hoppingStar hopping is a technique that is often used by amateur astronomers to locate objects in the night sky. It can be used in place of or in conjunction with setting circles.-The problem:...
Further reading
- Burnham's Celestial Handbook by Robert Burnham, Jr.Robert Burnham, Jr.Robert Burnham, Jr. was an American astronomer. He is best known for writing the classic three-volume Burnham's Celestial Handbook.-Early work:...
(Volume One, Volume Two, Volume Three at Google Books) - Deep Sky Observer's Guide by Neil Bone, Wil Tirion. Firefly Books, 2005. ISBN 1554070244.
- The practical astronomer's deep-sky companion by Jess K. Gilmour. Springer, 2003. ISBN 1852334746.
- Concise Catalog of Deep-sky Objects: Astrophysical Information for 500 Galaxies, Clusters and Nebulae by W. H. Finlay. London: Springer, 2003. ISBN 1-85233-691-9. Includes the Messier objects, Herschel 400 & more
- Visual astronomy of the deep sky by Roger Nelson Clark. CUP Archive, 1990. ISBN 0521361559.