Alkaid
  | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 13h 47m 32.43776s |
| Declination | +49° 18′ 47.7602″ |
| Apparent magnitude (V) | +1.86 |
| Characteristics | |
| Evolutionary stage | main sequence |
| Spectral type | B3 V |
| U−B color index | −0.68 |
| B−V color index | −0.19 |
| Astrometry | |
| Radial velocity (Rv) | −10.9 km/s |
| Proper motion (μ) | RA: −121.17 mas/yr Dec.: −14.91 mas/yr |
| Parallax (π) | 31.38±0.24 mas |
| Distance | 103.9 ± 0.8 ly (31.9 ± 0.2 pc) |
| Absolute magnitude (MV) | −0.67 |
| Details | |
| Mass | 5.071±0.023 M☉ |
| Radius | 2.894 (equatorial) 2.665 (polar) R☉ |
| Luminosity | 574 L☉ |
| Surface gravity (log g) | 3.78 cgs |
| Temperature | 16,329 (equatorial) 17,720 (polar) K |
| Rotation | 14.6 (equatorial) days 15.6 (polar) days |
| Rotational velocity (v sin i) | 154.3±9.1 km/s |
| Age | 6+2 −4 Myr |
| Other designations | |
| Alkaid, Benetnash, Benetnasch, Elkeid, η UMa, 85 UMa, BD+50°2027, FK5 509, GC 18643, HD 120315, HIP 67301, HR 5191, PPM 53742, SAO 44752. | |
| Database references | |
| SIMBAD | data |
Alkaid /ælˈkeɪd/, also called Eta Ursae Majoris (Latinised from η Ursae Majoris, abbreviated Eta UMa, η UMa), is a star in the constellation of Ursa Major. It is the easternmost star in the Big Dipper (or Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group. With an apparent visual magnitude of +1.86, it is the third-brightest star in the constellation and one of the brightest stars in the night sky.