Altair

From Wikipedia, the free encyclopedia

This article is about a star in the Aquila constellation. For other uses, see Altair (disambiguation).

**Altair**
Observation data Equinox J2000
Altair.
Constellation	Aquila
Right ascension	19h 50m 47.0s
Declination	+08° 52' 06"
Apparent magnitude (V)	0.77
Characteristics
Spectral type	A7 IV-V
U-B color index	0.08
B-V color index	0.22
Variable type	DelSct
Astrometry
Radial velocity (R_v)	−26.1 km/s
Proper motion (μ)	RA: 536.82 mas/yr Dec.: 385.54 mas/yr
Parallax (π)	194.97 ± 0.86 mas
Distance	16.73 ± 0.07 ly (5.13 ± 0.02 pc)
Absolute magnitude (M_V)	2.22
Details
Mass	1.7 M_☉
Radius	1.7 R_☉
Luminosity	10.7 L_☉
Temperature	8,000 K
Metallicity	200% Sun
Rotation	6.5–10.4 hours
Age	<10⁹ years
Other designations
α Aquilae, 53 Aquilae, HD 187642, HR 7557, BD+08°4236, GCTP 4665.00, GJ 768, LHS 3490, and HIP 97649.

Altair (α Aql / α Aquilae / Alpha Aquilae / Atair ) is the brightest star in the constellation Aquila and the twelfth brightest star in the nighttime sky, at visual magnitude 0.77.

Altair is a vertex of the Summer Triangle. It is an "A" type or white star located 17 light years away from Earth (about 99 trillion miles), one of the closest stars visible to the naked eye.

The name "Altair" is Arabic for "the Flying", from the phrase نسر الطائر an-nasr aţ-ţā?ir "the Flying Eagle". The spelling "Atair" is also used frequently.

It is officially known as 河鼓二 (Hégǔ'èr, the Second Star of the Drum at the River) in Chinese. However, it is more famous known as its other names: 牵牛星 or 牛郎星 (the Star of the Cowherd), after the Cowherd in the Chinese mythology: the Cowherd and the Weaver Girl.

Altair is most notable for its extremely rapid rotation; by measuring the width of its spectral lines, it was determined that its equator does a complete rotation in about 6½ hours (various other sources give 9 hours, or 10.4 hours). For comparison, our Sun requires just over 25 days for a complete rotation. As a result of its rapid rotation, Altair is oblate: its equatorial diameter is at least 14 percent greater than its polar diameter.

Altair, along with Beta Aquilae and Gamma Aquilae, form the well-known line of stars sometimes referred to as the shaft of Aquila.

1 References to the star
2 Location
3 See also
4 External links

[edit] References to the star

In Chinese mythology, there is a love story of Qi Xi in which Niu Lang (Altair) and his two children (Aquila -β and -γ) are separated forever from their mother Zhi Nü (Vega) who is on the far side of the river, the Milky Way. The Japanese Tanabata festival is also based on this legend.

In astrology, the star Altair was ill-omened, portending danger from reptiles.

In computing, an important early microcomputer, the Altair 8800, was named after the star because the daughter of the man responsible for coming up with a suitable name, when asked what she thought the computer should be called, was watching an episode of Star Trek where the Starship Enterprise had the star Altair as its destination. So Altair it was.

In space travel, Altair is the NASA Crew Exploration Vehicle (CEV) designed to travel to the Moon and International Space Station.