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'''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''', 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 an 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 has also be recently identified as [[variable star]], and thus has the New Suspected Variable designation '''NSV 24910'''.  The change in its magnitude is not possible to detect by the unaided eye.  The variation occurs in nine different periods ranging from nine hours to a mere 50 minutes in length, and changes by only a few thousandths of a magnitude.<ref>http://stars.astro.illinois.edu/sow/altair.html</ref>  

Altair has also be recently identified as [[variable star]], and thus has the New Suspected Variable designation '''NSV 24910'''.  The change in its magnitude is not possible to detect by the unaided eye.  The variation occurs in nine different periods ranging from nine hours to a mere 50 minutes in length, and changes by only a few thousandths of a magnitude.<ref>http://stars.astro.illinois.edu/sow/altair.html</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>

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 than 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 its 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.