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]
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- 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; et al. "Imaging the surface of Altair". Science. 317 (5836): 342–345. arXiv:0706.0867. Bibcode:2007Sci...317..342M. doi:10.1126/science.1143205. PMID 17540860. More than one of
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- 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.