Altair
Altair is the brightest star in the constellation of Aquila and the twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinised from α Aquilae and abbreviated Alpha Aql or α Aql. Altair is an A-type main-sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle asterism; the other two vertices are marked by Deneb and Vega. It is located at a distance of 16.7 light-years (5.1 parsecs) from the Sun.: 194 Altair is currently in the G-cloud—a nearby interstellar cloud, an accumulation of gas and dust.
| Observation data Epoch J2000.097 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Aquila |
| Pronunciation | /ˈæltɛər/, /ˈæltaɪər/ |
| Right ascension | 19h 50m 46.99855s |
| Declination | +08° 52′ 05.9563″ |
| Apparent magnitude (V) | 0.76 |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | A7Vn |
| U−B color index | +0.09 |
| B−V color index | +0.22 |
| V−R color index | +0.14 |
| R−I color index | +0.13 |
| Variable type | Delta Scuti |
| Astrometry | |
| Radial velocity (Rv) | −26.1±0.9 km/s |
| Proper motion (μ) | RA: +536.23 mas/yr Dec.: +385.29 mas/yr |
| Parallax (π) | 194.95 ± 0.57 mas |
| Distance | 16.73 ± 0.05 ly (5.13 ± 0.01 pc) |
| Absolute magnitude (MV) | 2.22 |
| Details | |
| Mass | 1.86±0.03 M☉ |
| Radius | 1.57 – 2.01 R☉ |
| Luminosity | 10.6 L☉ |
| Surface gravity (log g) | 4.29 cgs |
| Temperature | 6,860 – 8,621 K |
| Metallicity [Fe/H] | −0.2 dex |
| Rotation | 7.77 hours |
| Rotational velocity (v sin i) | 242 km/s |
| Age | 100 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Altair rotates rapidly, with a velocity at the equator of approximately 286 km/s. This is a significant fraction of the star's estimated breakup speed of 400 km/s. A study with the Palomar Testbed Interferometer revealed that Altair is not spherical, but is flattened at the poles due to its high rate of rotation. Other interferometric studies with multiple telescopes, operating in the infrared, have imaged and confirmed this phenomenon.