Altair
What is Altair?
Stars· Distance 16.7 ly · size 1.8× Sun (flattened by spin). The Cowherd star of the Tanabata legend and the southern corner of the Summer Triangle, facing Vega across the Milky Way. A nearby white star just 16.7 light-years away, it spins once every nine hours and bulges at the equator.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Altair is in your sky right now: https://nowsky.org/solar/sky?sel=altair — location and time set automatically, no login.
Distance and spectral type
Altair is about 17 light-years away, a white subgiant (spectral type A7IV-V), in the constellation Lyra. Its apparent magnitude is 0.8, visible to the naked eye.
Stellar figures
| Distance | 16.7 ly |
|---|---|
| Magnitude | 0.76 — twelfth brightest |
| Type | A7 white main-sequence |
| Rotation | 8.9 h (the Sun: 25 days) |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Behind the name
Arabic "the flying eagle". It spins so fast it bulges at the equator; in East Asia it is the Cowherd star.
Frequently asked
- How far is Altair from Earth?
- 16.7 ly.
- How bright is Altair (apparent magnitude)?
- 0.76 — twelfth brightest.
- What kind of object is Altair?
- A7 white main-sequence.
- How long is a day on Altair?
- 8.9 h (the Sun: 25 days).
- Which constellation is Altair in?
- Lyra.
- Where is Altair in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
The face of Altair, imaged in 2007
In 2007 the CHARA interferometer at Georgia State University combined the light of four telescopes to produce an image of Altair's surface — the first time the surface of any main-sequence star but the Sun had been directly imaged. The star in the image was an ellipse, not a circle, with a dark equator and bright poles: the flattening and gravity darkening caused by its 8.9-hour rotation, confirmed in a picture.
Altair's equatorial diameter is 22 percent greater than its polar, with temperatures computed at 6,900 °C at the equator and 8,500 at the poles. Because we see the star at a tilt, its bright poles and dark equator appear together in one frame, making it the specimen of what a fast rotator's surface looks like. Its nearness at 16.7 light-years and large angular size made the observation possible, and the method has since been applied to other fast spinners such as Vega and Regulus.
The star in depth
Altair, Alpha Aquilae, shines at magnitude 0.76 as the twelfth-brightest star in the night sky. At 16.7 light-years it is one of the nearest naked-eye stars, an A7 V white main-sequence star with 1.8 solar masses and eleven times the Sun's luminosity. In East Asia it is the Cowherd, facing the Weaver star Vega across the Milky Way in the Tanabata legend.
Its signature is rotation. Altair spins at 286 km/s at the equator, completing a turn every 8.9 hours — more than sixty times faster than the Sun's 25-day rotation. The equatorial diameter is about 22% larger than the polar diameter, and the poles are hotter than the equator through gravity darkening. In 2007 it became one of the first main-sequence stars whose surface was imaged directly with an interferometer, and the picture showed a visibly flattened ellipse.
From July to September it hangs high in the south-east to east on evenings, forming the Summer Triangle with Vega and Deneb; two fainter stars flank it, making it easy to identify. In the Sky view, set an August night to find Altair shining white at the southern edge of the Milky Way, and check its 16.7-light-year position in the 3D neighbourhood view.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.