ALTAIR, the 12th brightest star in the sky and the Alpha star of
Aquila is, however, the least luminous of the stars of the Summer
Triangle, which it makes with Vega and Deneb. 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.
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