Alpha Ursae Majoris
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| Observation data Equinox J2000 |
|
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 03m 43.7s |
| Declination | +61° 45′ 03″ |
| Apparent magnitude (V) | 1.79 (1.87/4.81/7.12) |
| Characteristics | |
| Spectral type | K0 III / F0 V / F8 |
| U-B color index | 0.92 |
| B-V color index | 1.07 |
| Variable type | Pulsating |
| Astrometry | |
| Radial velocity (Rv) | −9 km/s |
| Proper motion (μ) | RA: −136.46 mas/yr Dec.: −35.25 mas/yr |
| Parallax (π) | 26.38 ± 0.53 mas |
| Distance | 124 ± 2 ly (37.9 ± 0.8 pc) |
| Absolute magnitude (MV) | −1.09/1.83/4.22 |
| Visual binary orbit | |
| Companion | α UMa B |
| Period (P) | 44.4 a |
| Semimajor axis (a) | 0.603" |
| Eccentricity (e) | 0.4 |
| Inclination (i) | 152° |
| Node (Ω) | 2000° |
| Periastron epoch (T) | 1956.8 |
| Details | |
| Mass | 4/1.7 M☉ |
| Radius | 16/1.3 R☉ |
| Luminosity | 300 L☉ |
| Temperature | 4,500/7,400 K |
| Metallicity | ? |
| Rotation | <17 km/s. |
| Age | ? years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Ursae Majoris (α UMa / α Ursae Majoris) is the second-brightest star in the constellation of Ursa Major (despite its Bayer designation of "alpha"). It also has the traditional name Dubhe.
It forms part of the Big Dipper (also known as the Plough), and is the northern of the pointers, the two stars of Ursa Major which point towards Polaris. However, it is not part of the Ursa Major moving group. Instead, it is an evolved helium-burning star, about 124 light years away. It is a multiple star, orbited by a main sequence companion, Dubhe B, at a distance of about 23 astronomical units (AU), as well as a close pair, Dubhe C, at a distance of about 8000 AU.
The traditional name comes from the Arabic for "bear", dubb, from the phrase ظهر الدب الاكبر aż-żahr ad-dubb al-akbar "the back of the Greater Bear".
It is known as 北斗一 (the First Star of the Northern Dipper) or 天樞 (the Celestial Pivot) in Chinese.
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