Altair
Encyclopedia
Altair is the brightest star
in the constellation
Aquila
and the twelfth brightest star in the night sky. It is an A-type main sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle
; the other two are Deneb
and Vega
.
Altair rotates rapidly, with a velocity at the equator
of approximately 286 km/s.From values of v sin i and i in the second column of Table 1, Monnier et al. 2007. A study with the Palomar Testbed Interferometer
revealed that Altair is not spherical, but is flattened at the poles due to its high rate of rotation. Other interferometric studies with multiple telescopes, operating in the infrared
, have imaged and confirmed this phenomenon.
Altair is located 16.7 light-years (5.13 parsec
s) from Earth and is one of the closest stars visible to the naked eye. Along with Beta Aquilae and Gamma Aquilae, it forms the well-known line of stars sometimes referred to as the Family of Aquila or Shaft of Aquila.
Altair is a type-A main sequence star with approximately 1.8 times the mass
of the Sun and 11 times its luminosity. Altair possesses an extremely rapid rate of rotation; it has a rotational period of approximately 9 hours. For comparison, the equator of the Sun
requires just over 25 days for a complete rotation. This rapid rotation forces Altair to be oblate; its equatorial diameter is over 20 percent greater than its polar diameter.
Satellite measurements made in 1999 with the Wide Field Infrared Explorer
showed that the brightness of Altair fluctuates slightly, varying by less than a thousandth of a magnitude. As a result, it was identified in 2005 as a δ Scuti variable star. Its light curve
can be approximated by adding together a number of sine wave
s, with periods that range between 0.8 and 1.5 hours.
The angular diameter of Altair was measured interferometrically by R. Hanbury Brown and his co-workers at Narrabri Observatory
in the 1960s. They found a diameter of 3 milliarcseconds. Although Hanbury Brown et al. realized that Altair would be rotationally flattened, they had insufficient data to experimentally observe its oblateness. Altair was later observed to be flattened by infrared
interferometric measurements made by the Palomar Testbed Interferometer
in 1999 and 2000. This work was published by G. T. van Belle
and his co-authors in 2001.
Theory predicts that, owing to Altair's rapid rotation, its surface gravity
and effective temperature
should be lower at the equator, making the equator less luminous than the poles. This phenomenon, known as gravity darkening
or the von Zeipel effect, was confirmed for Altair by measurements made by the Navy Prototype Optical Interferometer
in 2001, and analyzed by Ohishi et al. (2004) and Peterson et al. (2006). Also, A. Domiciano de Souza et al. (2005) verified gravity darkening using the measurements made by the Palomar and Navy interferometers, together with new measurements made by the VINCI instrument at the VLTI.
Altair is one of the few stars for which a direct image has been obtained. In 2006 and 2007, J. D. Monnier and his coworkers produced an image of Altair's surface from 2006 infrared observations made with the MIRC instrument on the CHARA array
interferometer; this was the first time the surface of any main-sequence star, apart from the Sun
, had been imaged. The false-color image was published in 2007 and can be seen above and to the left; the brighter regions are shown in white and darker regions in blue. In this image, North (the direction towards the North Celestial Pole) is up and East is left, and the white line is the rotational axis of Altair. The black grid shows lines of latitude and longitude in an Altair-centric coordinate system. The von Zeipel effect can be observed in the image, which shows a white spot near the pole and a darker equator. The equatorial radius of the star was estimated to be 2.03 solar radii, and the polar radius 1.63 solar radii—a 25% increase of the stellar radius from pole to equator.
phrase , an-nasr aṭ-ṭā’ir (The flying eagle). The term Al Nesr Al Tair appeared in Al Achsasi Al Mouakket catalogue, which was translated into Latin
as Vultur Volans. This name was applied by the Arabs to the asterism
of α, β, and γ Aquilae and probably goes back to the ancient Babylonians and Sumerians, who called α Aquilae the eagle star. The spelling Atair has also been used.
The Koori
people of Victoria also knew Altair as Bunjil, the Wedge-tailed Eagle
, and β and γ Aquilae are his two wives the Black Swan
s. The people of the Murray River
knew the star as Totyerguil. The Murray River was formed when Totyerguil the hunter speared Otjout, a giant Murray Cod
, who, when wounded, churned a channel across southern Australia before entering the sky as the constellation Delphinus
.
In Chinese, the asterism consisting of α, β, and γ Aquilae is known as . Altair is thus known as . However, it is better known by its other names: or , or in English, Cowherd Star. These names are from the love story of , Qī Xī
, in which Niú Láng and his two children, β and γ Aquilae, are separated from their mother, , the star Vega
, by the Milky Way
. They are only permitted to meet once a year, when the Milky Way is crossed by a bridge of magpies. The Japanese festival, in which Altair is known as , is based on this legend.
The people of Micronesia
called Altair as Mai-lapa, "big/old breadfruit", while the Māori people called this star as Poutu-te-rangi, "pillar of heaven".
Japan Airlines
' Starjet 777-200 JA8983 was named Altair.
In astrology
, the star Altair was ill-omened, portending danger from reptile
s.
The NASA Constellation Program announced Altair as the name of the Lunar Surface Access Module
(LSAM) on December 13, 2007. The Russian-made Beriev Be-200 Altair
seaplane is also named after the star.
The 1956 science fiction film Forbidden Planet
is set on Altair IV, a presumed planet of the star.
The Altair 8800
was one of the first microcomputers intended for home use.
Altair is the name of three United States navy ships: , and .
designation WDS
19508+0852A and has three visual companion star
s, WDS
19508+0852B, C, and D. Component B is not physically close to A but merely appears close to it in the sky.
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 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....
Aquila
Aquila (constellation)
Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....
and the twelfth brightest star in the night sky. It is an A-type main sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle
Summer Triangle
The Summer Triangle is an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere's celestial sphere, with its defining vertices at Altair, Deneb, and Vega, being the brightest stars in the three constellations of Aquila, Cygnus, and Lyra.The English term was...
; the other two are 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...
and Vega
Vega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
.
Altair rotates rapidly, with a velocity at the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
of approximately 286 km/s.From values of v sin i and i in the second column of Table 1, Monnier et al. 2007. A study with the Palomar Testbed Interferometer
Palomar Testbed Interferometer
The Palomar Testbed Interferometer was a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was built by Caltech/JPL and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer...
revealed that Altair is not spherical, but is flattened at the poles due to its high rate of rotation. Other interferometric studies with multiple telescopes, operating 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...
, have imaged and confirmed this phenomenon.
Star
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s) from Earth and is one of the closest stars visible to the naked eye. Along with Beta Aquilae and Gamma Aquilae, it forms the well-known line of stars sometimes referred to as the Family of Aquila or Shaft of Aquila.
Altair is a type-A main sequence star with approximately 1.8 times the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the Sun and 11 times its luminosity. Altair possesses an extremely rapid rate of rotation; it has a rotational period of approximately 9 hours. For comparison, the equator 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...
requires just over 25 days for a complete rotation. This rapid rotation forces Altair to be oblate; its equatorial diameter is over 20 percent greater than its polar diameter.
Satellite measurements made in 1999 with the Wide Field Infrared Explorer
Wide Field Infrared Explorer
The Wide Field Infrared Explorer was a satellite launched on 5 March 1999 on the Pegasus XL rocket into a polar orbit between 409 km and 426 km above the Earth's surface...
showed that the brightness of Altair fluctuates slightly, varying by less than a thousandth of a magnitude. As a result, it was identified in 2005 as a δ Scuti variable star. Its light curve
Light curve
In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band...
can be approximated by adding together a number of sine wave
Sine wave
The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...
s, with periods that range between 0.8 and 1.5 hours.
Oblateness and surface temperature
Narrabri Stellar Intensity Interferometer
The Narrabri Stellar Intensity Interferometer was the first astronomical instrument to measure the diameters of a large number of stars at visible wavelengths. It was designed by Robert Hanbury Brown, who received the Hughes Medal in 1971 for this work...
in the 1960s. They found a diameter of 3 milliarcseconds. Although Hanbury Brown et al. realized that Altair would be rotationally flattened, they had insufficient data to experimentally observe its oblateness. Altair was later observed to be flattened by 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...
interferometric measurements made by the Palomar Testbed Interferometer
Palomar Testbed Interferometer
The Palomar Testbed Interferometer was a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was built by Caltech/JPL and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer...
in 1999 and 2000. This work was published by G. T. van Belle
Gerard van Belle
Gerard Theodore van Belle is an American astronomer. He received a bachelor's degree in physics from Whitman College in 1990, a master's in physics from The Johns Hopkins University in 1993, and a Ph.D. in physics from the University of Wyoming in 1996.Dr...
and his co-authors in 2001.
Theory predicts that, owing to Altair's rapid rotation, its surface gravity
Surface gravity
The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in...
and effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...
should be lower at the equator, making the equator less luminous than the poles. This phenomenon, known as gravity darkening
Gravity darkening
Gravity darkening, also referred to as Gravity Brightening, is an astronomical phenomenon where a star rotates so rapidly that it has a detectably oblate spheroid shape, such as in Regulus in the Leo constellation....
or the von Zeipel effect, was confirmed for Altair by measurements made by the Navy Prototype Optical Interferometer
Navy Prototype Optical Interferometer
The Navy Prototype Optical Interferometer , is an astronomical interferometer operated by the United States Naval Observatory Flagstaff Station, in collaboration with the Naval Research Laboratory and The Lowell Observatory...
in 2001, and analyzed by Ohishi et al. (2004) and Peterson et al. (2006). Also, A. Domiciano de Souza et al. (2005) verified gravity darkening using the measurements made by the Palomar and Navy interferometers, together with new measurements made by the VINCI instrument at the VLTI.
Altair is one of the few stars for which a direct image has been obtained. In 2006 and 2007, J. D. Monnier and his coworkers produced an image of Altair's surface from 2006 infrared observations made with the MIRC instrument on the CHARA array
CHARA array
The CHARA Array is an optical astronomical interferometer operated by The Center for High Angular Resolution Astronomy of the Georgia State University . CHARA is the World's highest angular resolution telescope at near-infrared wavelengths...
interferometer; this was the first time the surface of any main-sequence star, apart 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...
, had been imaged. The false-color image was published in 2007 and can be seen above and to the left; the brighter regions are shown in white and darker regions in blue. In this image, North (the direction towards the North Celestial Pole) is up and East is left, and the white line is the rotational axis of Altair. The black grid shows lines of latitude and longitude in an Altair-centric coordinate system. The von Zeipel effect can be observed in the image, which shows a white spot near the pole and a darker equator. The equatorial radius of the star was estimated to be 2.03 solar radii, and the polar radius 1.63 solar radii—a 25% increase of the stellar radius from pole to equator.
Etymology, mythology, and culture
The name Altair has been used since medieval times. It is an abbreviation of the ArabicArabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...
phrase , an-nasr aṭ-ṭā’ir (The flying eagle). The term Al Nesr Al Tair appeared in Al Achsasi Al Mouakket catalogue, which was translated into Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
as Vultur Volans. This name was applied by the Arabs to the asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
of α, β, and γ Aquilae and probably goes back to the ancient Babylonians and Sumerians, who called α Aquilae the eagle star. The spelling Atair has also been used.
The Koori
Koori
The Koori are the indigenous Australians that traditionally occupied modern day New South Wales and Victoria....
people of Victoria also knew Altair as Bunjil, the Wedge-tailed Eagle
Wedge-tailed Eagle
The Wedge-tailed Eagle , sometimes known as the Eaglehawk in its native range, is the largest bird of prey in Australia, but it is also found in southern New Guinea. It has long, fairly broad wings, fully feathered legs, and an unmistakable wedge-shaped tail...
, and β and γ Aquilae are his two wives the Black Swan
Black Swan
The Black Swan is a large waterbird, a species of swan, which breeds mainly in the southeast and southwest regions of Australia. The species was hunted to extinction in New Zealand, but later reintroduced. Within Australia they are nomadic, with erratic migration patterns dependent upon climatic...
s. The people of the Murray River
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...
knew the star as Totyerguil. The Murray River was formed when Totyerguil the hunter speared Otjout, a giant Murray Cod
Murray Cod
The Murray cod is a large Australian predatory freshwater fish of the Maccullochella genus and the Percichthyidae family. Although the species is a called cod in the vernacular, it is not related to the northern hemisphere marine cod species...
, who, when wounded, churned a channel across southern Australia before entering the sky as the constellation Delphinus
Delphinus
Delphinus is a constellation in the northern sky, close to the celestial equator. Its name is Latin for dolphin. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical...
.
In Chinese, the asterism consisting of α, β, and γ Aquilae is known as . Altair is thus known as . However, it is better known by its other names: or , or in English, Cowherd Star. These names are from the love story of , Qī Xī
Qi Xi
Qixi Festival , also known as Magpie Festival, falls on the seventh day of the seventh lunar month on the Chinese calendar; thus its name. It inspired Tanabata in Japan, Chilseok in Korea, and Thất Tịch in Vietnam...
, in which Niú Láng and his two children, β and γ Aquilae, are separated from their mother, , the star Vega
Vega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
, by 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...
. They are only permitted to meet once a year, when the Milky Way is crossed by a bridge of magpies. The Japanese festival, in which Altair is known as , is based on this legend.
The people of Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
called Altair as Mai-lapa, "big/old breadfruit", while the Māori people called this star as Poutu-te-rangi, "pillar of heaven".
Japan Airlines
Japan Airlines
is an airline headquartered in Shinagawa, Tokyo, Japan. It is the flag carrier of Japan and its main hubs are Tokyo's Narita International Airport and Tokyo International Airport , as well as Nagoya's Chūbu Centrair International Airport and Osaka's Kansai International Airport...
' Starjet 777-200 JA8983 was named Altair.
In astrology
Astrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...
, the star Altair was ill-omened, portending danger from reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s.
The NASA Constellation Program announced Altair as the name of the Lunar Surface Access Module
Lunar Surface Access Module
The Altair spacecraft, previously known as the Lunar Surface Access Module or LSAM, was the planned lander spacecraft component of NASA's cancelled Project Constellation. Astronauts would have used the spacecraft for landings on the Moon, which had been intended to begin around 2019...
(LSAM) on December 13, 2007. The Russian-made Beriev Be-200 Altair
Beriev Be-200
The Beriev Be-200 Altair is a multipurpose amphibious aircraft designed by the Beriev Aircraft Company and manufactured by Irkut. Marketed as being designed for fire fighting, search and rescue, maritime patrol, cargo, and passenger transportation, it has a capacity of 12 tonnes of water, or up...
seaplane is also named after the star.
The 1956 science fiction film Forbidden Planet
Forbidden Planet
Forbidden Planet is a 1956 science fiction film directed by Fred M. Wilcox, with a screenplay by Cyril Hume. It stars Leslie Nielsen, Walter Pidgeon, and Anne Francis. The characters and its setting have been compared to those in William Shakespeare's The Tempest, and its plot contains certain...
is set on Altair IV, a presumed planet of the star.
The Altair 8800
Altair 8800
The MITS Altair 8800 was a microcomputer design from 1975 based on the Intel 8080 CPU and sold by mail order through advertisements in Popular Electronics, Radio-Electronics and other hobbyist magazines. The designers hoped to sell only a few hundred build-it-yourself kits to hobbyists, and were...
was one of the first microcomputers intended for home use.
Altair is the name of three United States navy ships: , and .
Visual companions
The A-type main sequence star has the multiple starMultiple star
A multiple star consists of three or more stars which appear from the Earth to be close to one another in the sky. This may result from the stars being physically close and gravitationally bound to each other, in which case it is physical, or this closeness may be merely apparent, in which case...
designation 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...
19508+0852A and has three visual companion 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, 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...
19508+0852B, C, and D. Component B is not physically close to A but merely appears close to it in the sky.
External links
- Star with Midriff Bulge Eyed by Astronomers, JPL press release, July 25, 2001.
- Imaging the Surface of Altair, University of Michigan news release detailing the CHARA array direct imaging of the stellar surface in 2007.
- PIA04204: Altair, NASA. Image of Altair from the Palomar Testbed InterferometerPalomar Testbed InterferometerThe Palomar Testbed Interferometer was a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was built by Caltech/JPL and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer...
. - Altair at SolStation.
- Secrets of Sun-like star probed, BBC News, June 1, 2007.
- Astronomers Capture First Images of the Surface Features of Altair, astromart.com.
- Image of Altair from AladinAladin Sky AtlasAladin is an interactive software sky atlas allowing the user to visualize digitized astronomical images, superimpose entries from astronomical catalogues or databases, and interactively access related data and information from the SIMBAD database, the VizieR service and other archives for all...
.