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. 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). 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 spins rapidly, with a velocity at its equator of about 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 showed 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 confirmed this.
References[change | change source]
- "Our Local Galactic Neighborhood". NASA.
- Gilster, Paul (2010-09-01). "Into the Interstellar Void". Centauri Dreams. Retrieved 2017-03-26.
- Summer Triangle, entry, The Internet Encyclopedia of Science, David Darling. Accessed on line November 26, 2008.
- Hoboken, Fred Schaaf (2008). The brightest stars : discovering the universe through the sky's most brilliant stars. New Jersey: John Wiley & Sons, Inc. p. 194. ISBN 978-0-471-70410-2. OCLC 440257051.
- From values of v sin i and i in the second column of Table 1, Monnier et al. 2007.
- Monnier J D. et al 2007. "Imaging the surface of Altair". Science 317 (5836): 342–345. doi:10.1126/science.1143205. PMID 17540860.
- Robrade J. & Schmitt J.H.M.M. 2009. Altair - the "hottest" magnetically active star in X-rays. Astronomy and Astrophysics, 497 (2): 511–520
- Belle, Gerard T. van et al (2001). "Altair's oblateness and rotation velocity from long-baseline interferometry" (in en). The Astrophysical Journal 559 (2): 1155–1164. doi:10.1086/322340. ISSN 0004-637X. http://stacks.iop.org/0004-637X/559/i=2/a=1155.