Altair

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Altair (Alpha Aquilae / Alpha Aql / α Aquilae / α Aql / Atair) 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.[1][5][7]

Altair rotates rapidly, with a velocity at the equator of approximately 286 km/s.[nb 3][3] 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.[8] Other interferometric studies with multiple telescopes, operating in the infrared, have imaged and confirmed this phenomenon.[3]

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Star

Altair is located 16.8 light-years (5.14 parsecs) from Earth and is one of the closest stars visible to the naked eye.[9] 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.[10]

Altair is a type-A main sequence star with approximately 1.8 times the mass of the Sun and 11 times its luminosity.[3][4] Altair possesses an extremely rapid rate of rotation; it has a rotational period of approximately 9 hours.[4] 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.[3]

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