Alpha Gruis
 Location of α Gruis (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Grus |
| Right ascension | 22h 08m 13.98473s |
| Declination | –46° 57′ 39.5078″ |
| Apparent magnitude (V) | +1.74 |
| Characteristics | |
| Spectral type | B6 V |
| U−B color index | –0.47 |
| B−V color index | –0.13 |
| Astrometry | |
| Radial velocity (Rv) | +11.8 km/s |
| Proper motion (μ) |
RA: +126.69 mas/yr Dec.: −147.47 mas/yr |
| Parallax (π) | 32.29 ± 0.21mas |
| Distance | 101.0 ± 0.7 ly (31.0 ± 0.2 pc) |
| Details | |
| Mass | 4.0 M☉ |
| Radius | 3.4 R☉ |
| Luminosity | 263 L☉ |
| Surface gravity (log g) | 3.76 ± 0.11 cgs |
| Temperature | 13,920 K |
| Metallicity [Fe/H] | –0.13 ± 0.02 dex |
| Rotational velocity (v sin i) | 215 km/s |
| Age | 0.10 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Gruis (α Gruis, abbreviated Alpha Gru, α Gru), also named Alnair, is the brightest star in the southern constellation of Grus.
α Gruis (Latinised to Alpha Gruis) is the star's Bayer designation. (Its first depiction in a celestial atlas was in Johann Bayer's Uranometria of 1603.)
It bore the traditional name Alnair or Al Nair (sometimes Al Na'ir in lists of stars used by navigators), from the Arabic al-nayyir [an-nai:r], meaning "the bright one", itself derived from its Arabic name, al-Nayyir min Dhanab al-ḥūt (al-Janūbiyy), "the Bright (star) belongs to the Tail of (the constellation of) the (Southern) Fish". Confusingly, Alnair was also given as the proper name for Zeta Centauri in an astronomical ephemerides in the middle of the 20th century. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name Alnair for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.
With Beta, Delta, Theta, Iota, and Lambda Gruis, Alnair belonged to Piscis Austrinus in traditional Arabic astronomy.
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