Altair (Alpha Aquilae)
Altair (Alpha Aquilae) is a star in the constellation Aquila, magnitude 0.8.
A star that spins once in under eight hours — so fast it has been squashed into a flattened ball.
Altair spins once in under eight hours; the Sun takes about 25 days. That whirl, faster even than Jupiter’s, flattens the star so that its equator is more than 20% wider than its poles. The poles are hotter and brighter than its middle, an effect called gravity darkening. In 2007 Altair became the first ordinary, hydrogen-burning star besides the Sun to have the details of its surface imaged, using the CHARA array of telescopes.
It is a young star of about 100 million years, with 1.8 times the Sun’s mass and 11 times its light. Its name comes from the Arabic al-nasr al-ṭā’ir, ‘the flying eagle’. In the Chinese and Japanese legend it is the Cowherd, Niulang or Hikoboshi, with the two stars beside him as his children — kept apart from his wife, Vega, by the river of the Milky Way.
Altair (Alpha Aquilae) is 16.7 light-years away: the light we see from it set off in 2009, 3 years after Pluto was reclassified as a dwarf planet.
Did you know?
- Calling Altair. In 1983 a group of Japanese scientists beamed a radio message towards Altair, hoping to reach anyone who might be listening.
- Bunjil the eagle. The Koori people of Victoria know Altair as Bunjil, the wedge-tailed eagle. The two stars beside it are his wives, the black swans.
- A gentle flicker. Altair brightens and dims by a few thousandths of a magnitude, with several rhythms each under two hours long. It was classed as a Delta Scuti variable in 2005.
A bright white star with a fainter star close on each side, forming a short line — the eagle of Aquila. It marks one corner of the big triangle with Vega and Deneb. Its two flanking stars make it easy to confirm.
When and where to see it
It is best placed in the evening sky around August, when it crosses the meridian at about 10 pm local time (around midnight in July). It can be seen from everywhere north of 81°S and never sets north of 81°N.
At its highest it stands 49° up from 50°N, 64° up from 35°N, 81° up from the equator, 46° up from 35°S.
Facts
- Type
- Star
- Constellation
- Aquila
- Designations
- Alpha Aquilae, α Aql, 53 Aql, HR 7557, HD 187642, HIP 97649
- Magnitude
- 0.8
- Position
- RA 19h 50.8m, Dec +8° 52′ (J2000)
- Spectral type
- A7Vn
- Colour
- yellow-white (B−V 0.22)
- Distance
- 16.7 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Altair (Alpha Aquilae) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.