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[[File:Aquila constellation map.png|300px|right|thumb|Location and position of Altair]]   

[[File:Aquila constellation map.png|300px|right|thumb|Location and position of Altair]]   

'''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<ref name="simbad">http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+aql</ref>, making it readily visible to the unaided eye.  

'''Altair''', also known as '''Alpha Aquilae''', is a spectral class A star located 16.8 light years away in the constellation [[Aquila]] as its 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<ref name="simbad">http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+aql</ref>, making it readily visible to the unaided eye.  

==Altair in history==

==Altair in history==

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 its 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 its hydrogen fuel within a billion years due to its 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<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>.

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 its surface, is centered around 3.4 AU.

[[Category:Astronomy]]

[[Category:Astronomy]]