Altair (), also designated Alpha Aquilae (α Aquilae, abbreviated Alpha Aql, α Aql), is the brightest star in the constellation of Aquila and the twelfth brightest star in the night sky. It is currently in the G-cloud—a nearby accumulation of gas and dust known as an interstellar cloud. Altair is an A-type main sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the asterism known as the Summer Triangle (the other two vertices are marked by Deneb and Vega). It is 16.7 light-years (5.13 parsecs) from the Sun and is one of the closest stars visible to the naked eye. Altair rotates rapidly, with a velocity at the equator of approximately 286 km/s. This is a significant fraction of the star's estimated breakup speed of 400 km/s. 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.
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