Altair
Brightest star in the constellation Aquila / From Wikipedia, the free encyclopedia
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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.[7][14][15] It is located at a distance of 16.7 light-years (5.1 parsecs) from the Sun.[16]: 194 Altair is currently in the G-cloud—a nearby interstellar cloud, an accumulation of gas and dust.[17][18]
Observation data Epoch J2000.097 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Aquila |
Pronunciation | /ˈæltɛər/, /ˈæltaɪər/[1][2] |
Right ascension | 19h 50m 46.99855s[3] |
Declination | +08° 52′ 05.9563″[3] |
Apparent magnitude (V) | 0.76[4] |
Characteristics | |
Evolutionary stage | Main sequence |
Spectral type | A7Vn[5] |
U−B color index | +0.09[4] |
B−V color index | +0.22[4] |
V−R color index | +0.14[4] |
R−I color index | +0.13[4] |
Variable type | Delta Scuti[6] |
Astrometry | |
Radial velocity (Rv) | −26.1±0.9[7] km/s |
Proper motion (μ) | RA: +536.23[3] mas/yr Dec.: +385.29[3] mas/yr |
Parallax (π) | 194.95 ± 0.57 mas[3] |
Distance | 16.73 ± 0.05 ly (5.13 ± 0.01 pc) |
Absolute magnitude (MV) | 2.22[6] |
Details | |
Mass | 1.86±0.03[8] M☉ |
Radius | 1.57 – 2.01[8][nb 1] R☉ |
Luminosity | 10.6[9] L☉ |
Surface gravity (log g) | 4.29[10] cgs |
Temperature | 6,860 – 8,621[8][nb 1] K |
Metallicity [Fe/H] | −0.2[11] dex |
Rotation | 7.77 hours[9] |
Rotational velocity (v sin i) | 242[8] km/s |
Age | 100[8] Myr |
Other designations | |
Database references | |
SIMBAD | data |
Altair rotates rapidly, with a velocity at the equator of approximately 286 km/s.[nb 2][11] This is a significant fraction of the star's estimated breakup speed of 400 km/s.[19] 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.[20] Other interferometric studies with multiple telescopes, operating in the infrared, have imaged and confirmed this phenomenon.[11]