Mizar
Mizar /ˈmaɪzɑːr/ is a second-magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major. It has the Bayer designation ζ Ursae Majoris (Latinised as Zeta Ursae Majoris). It forms a well-known naked eye double star with the fainter star Alcor, and is itself a quadruple star system. The Mizar and Alcor system lies about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite, and is part of the Ursa Major Moving Group.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| Mizar | |
| Right ascension | 13h 23m 55.54048s |
| Declination | +54° 55′ 31.2671″ |
| Apparent magnitude (V) | 2.04 |
| ζ1 UMa | |
| Right ascension | 13h 23m 55.543s |
| Declination | +54° 55′ 31.30″ |
| Apparent magnitude (V) | 2.23 |
| ζ2 UMa | |
| Right ascension | 13h 23m 56.330s |
| Declination | +54° 55′ 18.56″ |
| Apparent magnitude (V) | 3.88 |
| Characteristics | |
| ζ1 UMa | |
| Spectral type | A2Vp/A2Vp |
| U−B color index | −0.01 |
| B−V color index | +0.02 |
| ζ2 UMa | |
| Spectral type | kA1h(eA)mA7IV-V |
| U−B color index | +0.09 |
| B−V color index | +0.13 |
| Astrometry | |
| Radial velocity (Rv) | −6.31 km/s |
| Proper motion (μ) | RA: 119.01 mas/yr Dec.: −25.97 mas/yr |
| Parallax (π) | 39.36 ± 0.30 mas |
| Distance | 82.9 ± 0.6 ly (25.4 ± 0.2 pc) |
| Absolute magnitude (MV) | +0.32/+1.96 |
| Orbit | |
| Primary | Mizar Aa |
| Companion | Mizar Ab |
| Period (P) | 20.5386 days |
| Semi-major axis (a) | 9.83±0.03 mas |
| Eccentricity (e) | 0.5415±0.0016 |
| Inclination (i) | 60.5±0.3° |
| Longitude of the node (Ω) | 106.0±0.4° |
| Periastron epoch (T) | RJD 54536.9904 |
| Argument of periastron (ω) (secondary) | 105.27±0.23° |
| Semi-amplitude (K1) (primary) | 66.478±0.153 km/s |
| Semi-amplitude (K2) (secondary) | 66.019±0.177 km/s |
| Orbit | |
| Primary | Mizar Ba |
| Companion | Mizar Bb |
| Period (P) | 175.55 d |
| Semi-major axis (a) | 29.849 mas |
| Eccentricity (e) | 0.46 |
| Details | |
| Mizar Aa | |
| Mass | 2.2224±0.0221 M☉ |
| Radius | 2.4 ± 0.1 R☉ |
| Luminosity | 33.3 ± 2.1 L☉ |
| Temperature | 9,000 ± 200 K |
| Age | 370 Myr |
| Mizar Ab | |
| Mass | 2.2381±0.0219 M☉ |
| Radius | 2.4 ± 0.1 R☉ |
| Luminosity | 33.3 ± 2.1 L☉ |
| Temperature | 9,000 ± 200 K |
| ζ2 UMa | |
| Surface gravity (log g) | 4.40 cgs |
| Temperature | 8,425 K |
| Rotational velocity (v sin i) | 61 km/s |
| Other designations | |
| ζ1 UMa: GC 18133, HD 116656, HR 5054, PPM 34007, SAO 28737 | |
| ζ2 UMa: GC 18134, HD 116657, HR 5055, SAO 28738 | |
| Database references | |
| SIMBAD | Mizar |
| ζ1 UMa | |
| ζ2 UMa | |
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