Difference between revisions of "Altair"
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==Altair in history== | ==Altair in history== | ||
| − | The common name of Altair is derived from the [[Arabic]] phase النسر الطائر, ''an-nasr aţ-ţā’ir'' or "The Flying Eagle", the name has been in use since the Medieval Era. Originally the Arabic phrase applied to the pattern Altair formed along with Beta and Gamma Aquilae. The idea of Altair as the eagle or part of the eagle possibly goes back to ancient Babylon or Sumeria, as both civilizations referred to the star as the eagle star<ref name="myth">>pp. 17–18, A Dictionary of Modern Star Names, Paul Kunitzsch and Tim Smart, Cambridge, Massachusetts: Sky Publishing, 2006, ISBN 978-1-931559-44-7.</ref>. | + | The common name of Altair is derived from the [[Arabic]] phase النسر الطائر, ''an-nasr aţ-ţā’ir'' or "The Flying Eagle", the name has been in use since the Medieval Era. Originally the Arabic phrase applied to the pattern Altair formed along with Beta and Gamma Aquilae. The idea of Altair as the eagle or as a part of the eagle possibly goes back to ancient Babylon or Sumeria, as both civilizations referred to the star as the eagle star<ref name="myth">>pp. 17–18, A Dictionary of Modern Star Names, Paul Kunitzsch and Tim Smart, Cambridge, Massachusetts: Sky Publishing, 2006, ISBN 978-1-931559-44-7.</ref>. |
The [[Chinese]] referred to Altair itself as 河鼓二 (''Hé Gŭ èr'' or Second Star of the Drum at the River) due to the asterism the star formed along with Beta and Gamma Aquilae called 河鼓 (''Hé Gŭ'' or River Drum)<ref name="myth">>pp. 17–18, A Dictionary of Modern Star Names, Paul Kunitzsch and Tim Smart, Cambridge, Massachusetts: Sky Publishing, 2006, ISBN 978-1-931559-44-7.</ref>. However the star was also commonly called 牛郎星 (''Niú Láng Xīng'' or Star of the Cowhead), where it is associated with Chinese [[mythology]] in reference to the stars. In [[Japan]], Altair has a similar name 彦星 (''Hikoboshi'', or Cow Herder Star), based on the same [[mythology]]<ref>p. 72, China, Japan, Korea Culture and Customs: Culture and Customs, Ju Brown and John Brown, 2006, ISBN 9781419648939.</ref>. | The [[Chinese]] referred to Altair itself as 河鼓二 (''Hé Gŭ èr'' or Second Star of the Drum at the River) due to the asterism the star formed along with Beta and Gamma Aquilae called 河鼓 (''Hé Gŭ'' or River Drum)<ref name="myth">>pp. 17–18, A Dictionary of Modern Star Names, Paul Kunitzsch and Tim Smart, Cambridge, Massachusetts: Sky Publishing, 2006, ISBN 978-1-931559-44-7.</ref>. However the star was also commonly called 牛郎星 (''Niú Láng Xīng'' or Star of the Cowhead), where it is associated with Chinese [[mythology]] in reference to the stars. In [[Japan]], Altair has a similar name 彦星 (''Hikoboshi'', or Cow Herder Star), based on the same [[mythology]]<ref>p. 72, China, Japan, Korea Culture and Customs: Culture and Customs, Ju Brown and John Brown, 2006, ISBN 9781419648939.</ref>. | ||
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==The Star== | ==The Star== | ||
| − | Altair is a white main sequence star of spectral class A7 V-IV<ref name="simbad">http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+aql</ref>. The star is estimated to have some 1.7 times the mass of our sun, and 1.8 times its diameter<ref>Imaging the Surface of Altair, J. Monnier et al., Science 317, #5836 (July 20, 2007), pp. 342–345</ref>. Altair is also considerably brighter with 10.7 times the visual luminosity of the Sun, even though much of the [[radiation]] from Altair is in the [[ultraviolet]]. | + | Altair is a white main sequence star of spectral class A7 V-IV<ref name="simbad">http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+aql</ref>. The star is estimated to have some 1.7 times the mass of our sun, and 1.8 times its diameter<ref>Imaging the Surface of Altair, J. Monnier et al., Science 317, #5836 (July 20, 2007), pp. 342–345</ref>. Altair is also considerably brighter, with 10.7 times the visual luminosity of the Sun, even though much of the [[radiation]] from Altair is in the [[ultraviolet]]. |
Altair is a young, [[metallicity|metals-rich star]]. Using [[metallicity]], the star is estimated to be twice as enriched as the [[Sun]], based on it's abundance of [[iron]]<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1992A%26AS...95..273C</ref>. Dust has been also detected orbiting Altair<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...350..603H&db_key=AST&high=3faa46c3cc22628</ref>. The star itself may only be a few hundred million years old but will quickly exhaust it's hydrogen fuel within a billion years due to it's size and temperature. | Altair is a young, [[metallicity|metals-rich star]]. Using [[metallicity]], the star is estimated to be twice as enriched as the [[Sun]], based on it's abundance of [[iron]]<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1992A%26AS...95..273C</ref>. Dust has been also detected orbiting Altair<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...350..603H&db_key=AST&high=3faa46c3cc22628</ref>. The star itself may only be a few hundred million years old but will quickly exhaust it's hydrogen fuel within a billion years due to it's size and temperature. | ||
| − | One interesting aspect about Altair is the unusually fast rotational | + | One interesting aspect about Altair is the unusually fast rotational speed of 210 kilometers per second. The star rotates so quickly that it completes a rotation in some 10.4 hours. In comparison, the [[Sun]] takes 25.4 days to complete a rotation. As a result of this rapid rotation, the star is most likely shaped like a flattened ellipsoid, with an equatorial diameter some 14 percent greater then the diameter at the poles<ref>Altair's Oblateness and Rotation Velocity from Long-Baseline Interferometry, Gerard T. van Belle, David R. Ciardi, Robert R. Thompson, Rachel L. Akeson, and Elizabeth A. Lada, Astrophysical Journal 559 (October 1, 2001), pp. 1155–1164, doi:10.1086/322340, Bibcode: 2001ApJ...559.1155</ref>. |
| − | So far no substellar companions have been detected around Altair. Altair's [[habitable zone]], where an [[Earth|Earth-like]] world could have liquid water on it's surface, is centered around 3.4 AU. | + | So far, no substellar companions have been detected around Altair. Altair's [[habitable zone]], where an [[Earth|Earth-like]] world could have liquid water on it's surface, is centered around 3.4 AU. |
[[Category:Astronomy]] | [[Category:Astronomy]] | ||
Revision as of 20:08, July 15, 2009
Altair, also known as Alpha Aquilae, is a spectral class A star located 16.8 light years away in the constellation Aquila as it's brightest star. Altair is also the lower left member of the Summer Triangle. The star is the 12th brightest in the night sky with a apparent magnitude of 0.77[1], making it readily visible to the unaided eye.
Altair in history
The common name of Altair is derived from the Arabic phase النسر الطائر, an-nasr aţ-ţā’ir or "The Flying Eagle", the name has been in use since the Medieval Era. Originally the Arabic phrase applied to the pattern Altair formed along with Beta and Gamma Aquilae. The idea of Altair as the eagle or as a part of the eagle possibly goes back to ancient Babylon or Sumeria, as both civilizations referred to the star as the eagle star[2].
The Chinese referred to Altair itself as 河鼓二 (Hé Gŭ èr or Second Star of the Drum at the River) due to the asterism the star formed along with Beta and Gamma Aquilae called 河鼓 (Hé Gŭ or River Drum)[2]. However the star was also commonly called 牛郎星 (Niú Láng Xīng or Star of the Cowhead), where it is associated with Chinese mythology in reference to the stars. In Japan, Altair has a similar name 彦星 (Hikoboshi, or Cow Herder Star), based on the same mythology[3].
The Star
Altair is a white main sequence star of spectral class A7 V-IV[1]. The star is estimated to have some 1.7 times the mass of our sun, and 1.8 times its diameter[4]. Altair is also considerably brighter, with 10.7 times the visual luminosity of the Sun, even though much of the radiation from Altair is in the ultraviolet.
Altair is a young, metals-rich star. Using metallicity, the star is estimated to be twice as enriched as the Sun, based on it's abundance of iron[5]. Dust has been also detected orbiting Altair[6]. The star itself may only be a few hundred million years old but will quickly exhaust it's hydrogen fuel within a billion years due to it's size and temperature.
One interesting aspect about Altair is the unusually fast rotational speed of 210 kilometers per second. The star rotates so quickly that it completes a rotation in some 10.4 hours. In comparison, the Sun takes 25.4 days to complete a rotation. As a result of this rapid rotation, the star is most likely shaped like a flattened ellipsoid, with an equatorial diameter some 14 percent greater then the diameter at the poles[7].
So far, no substellar companions have been detected around Altair. Altair's habitable zone, where an Earth-like world could have liquid water on it's surface, is centered around 3.4 AU.
References
- ↑ 1.0 1.1 http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+aql
- ↑ 2.0 2.1 >pp. 17–18, A Dictionary of Modern Star Names, Paul Kunitzsch and Tim Smart, Cambridge, Massachusetts: Sky Publishing, 2006, ISBN 978-1-931559-44-7.
- ↑ p. 72, China, Japan, Korea Culture and Customs: Culture and Customs, Ju Brown and John Brown, 2006, ISBN 9781419648939.
- ↑ Imaging the Surface of Altair, J. Monnier et al., Science 317, #5836 (July 20, 2007), pp. 342–345
- ↑ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1992A%26AS...95..273C
- ↑ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...350..603H&db_key=AST&high=3faa46c3cc22628
- ↑ Altair's Oblateness and Rotation Velocity from Long-Baseline Interferometry, Gerard T. van Belle, David R. Ciardi, Robert R. Thompson, Rachel L. Akeson, and Elizabeth A. Lada, Astrophysical Journal 559 (October 1, 2001), pp. 1155–1164, doi:10.1086/322340, Bibcode: 2001ApJ...559.1155