star in the constellation Aquila

Altair, also called α Aquilae, α Aql, is the brightest star in the constellation of Aquila.

It is the twelfth brightest star in the night sky. It is in the G-cloud—a fog of gas and dust known as an interstellar cloud.[1][2] Altair is an A-type main sequence star with an apparent visual magnitude of 0.77. It is one of the vertices of the Summer Triangle (the other two vertices are Deneb and Vega).[3] It is 16.7 light-years (5.13 parsecs) from the Sun and is one of the closest stars visible to the naked eye.[4]

Altair spins rapidly, with a velocity at its equator of about 286 km/s.[5][6] This is a significant fraction of the star's estimated breakup speed of 400 km/s.[7] A study with the Palomar Testbed Interferometer showed 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 confirmed this.[6]


  1. "Our Local Galactic Neighborhood". NASA. Archived from the original on 2013-11-21.
  2. Gilster, Paul (2010-09-01). "Into the Interstellar Void". Centauri Dreams. Retrieved 2017-03-26.
  3. Summer Triangle, entry, The Internet Encyclopedia of Science, David Darling. Accessed on line November 26, 2008.
  4. Hoboken, Fred Schaaf (2008). The brightest stars : discovering the universe through the sky's most brilliant stars. New Jersey: John Wiley & Sons, Inc. pp. 194. ISBN 978-0-471-70410-2. OCLC 440257051.
  5. From values of v sin i and i in the second column of Table 1, Monnier et al. 2007.
  6. 6.0 6.1 Monnier J D.; et al. (2007). "Imaging the surface of Altair". Science. 317 (5836): 342–345. arXiv:0706.0867. Bibcode:2007Sci...317..342M. doi:10.1126/science.1143205. PMID 17540860. S2CID 4615273.
  7. Robrade J. & Schmitt J.H.M.M. 2009. Altair - the "hottest" magnetically active star in X-rays. Astronomy and Astrophysics, 497 (2): 511–520
  8. Belle, Gerard T. van; et al. (2001). "Altair's oblateness and rotation velocity from long-baseline interferometry". The Astrophysical Journal. 559 (2): 1155–1164. Bibcode:2001ApJ...559.1155V. doi:10.1086/322340. ISSN 0004-637X. S2CID 13969695.[permanent dead link]