Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.

ALTAIR

First magnitude Altair, the 12th brightest star in the sky and the Alpha star of Aquila the Eagle, is also the southern anchor of the famed Summer Triangle, which it makes with Vega and Deneb. The Arabic name "Altair," reflective of the constellation itself, comes from a phrase meaning "the flying eagle." Though the constellation does not look much like its name, Altair itself is flanked by a pair of stars (the Beta and Gamma stars Alshain and Tarazed) that really do remind the sky-gazer of a bird with outstretched wings. The trio of stars has in fact been taken for an airplane with wing lights slowly flying across the sky. Though three of the stars of the Summer Triangle are all white in color and hotter than the Sun, all are also individuals. With a temperature of about 7800 degrees Kelvin, Altair is the coolest of the three (with Vega and Deneb nearly equal at 9500 Kelvin). Altair is also the least luminous. From its distance of 16.8 light years, we find it to be 11 times brighter than the Sun, as opposed to 50 times for Vega and an astounding 200,000 or so for much more distant Deneb. Like the Sun and Vega, Altair is "on the main sequence" of stars, fusing hydrogen into helium in its core. Yet the star is not without its own striking characteristics. It is moving across the sky against the background of distant stars more quickly than most, and will displace itself by as much as a degree in only 5000 years. It is also a very rapid rotator. Its equatorial spin speed, while certainly not a record, is still an astonishing 242 kilometers per second, as compared with the Sun's 2 kilometers per second. With its radius about 1.7 times that of the Sun, the star has a rotation period of only 9 hours, as opposed to nearly a month for our ponderously spinning Sun.