Dubhe
Dubhe /ˈdʌbiː/, also called Alpha Ursae Majoris, Latinised from α Ursae Majoris, is, despite being designated "α" (alpha), the second-brightest object in the northern constellation of Ursa Major. This prominent asterism is known as the Big Dipper, the Plough, and the Great Bear. Alpha Ursae Majoris is the northern of the 'pointers' (or 'guards'), the second being Beta Ursae Majoris, or 'Merak' – this pair of stars point towards Polaris, the North Star.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 03m 43.67152s |
| Declination | +61° 45′ 03.7249″ |
| Apparent magnitude (V) | 1.79 |
| Characteristics | |
| Spectral type | K0III + F0V |
| U−B color index | +0.93 |
| B−V color index | +1.07 |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | −9.4±0.3 km/s |
| Proper motion (μ) | RA: –134.11 mas/yr Dec.: –34.70 mas/yr |
| Parallax (π) | 26.54 ± 0.48 mas |
| Distance | 123 ± 2 ly (37.7 ± 0.7 pc) |
| Absolute magnitude (MV) | −1.10±0.04 |
| Orbit | |
| Companion | α UMa B |
| Period (P) | 44.45±0.11 yr |
| Semi-major axis (a) | 0.590±0.026″ |
| Eccentricity (e) | 0.439±0.004 |
| Inclination (i) | 159.9±3.5° |
| Longitude of the node (Ω) | 9.3±8.2° |
| Periastron epoch (T) | 2,002.17±0.09 |
| Argument of periastron (ω) (secondary) | 232.8±7.9° |
| Details | |
| α UMa A | |
| Mass | 3.44±0.11 M☉ |
| Radius | 17.03±0.13 R☉ |
| Luminosity | 165.1±8.3 L☉ |
| Surface gravity (log g) | 2.20 cgs |
| Temperature | 5,012±65 K |
| Metallicity [Fe/H] | −0.20±0.07 dex |
| Rotational velocity (v sin i) | 2.6±1.0 km/s |
| Age | 280±30 Myr |
| α UMa B | |
| Mass | ~1.6 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
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