Mizar

This article is about the star. For other uses, see Mizar (disambiguation). For a star also called Mizar, see Epsilon Boötis.
Mizar
Location of Mizar (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Mizar
Right ascension 13h 23m 55.54048s[1]
Declination +54° 55′ 31.2671″[1]
Apparent magnitude (V) 2.04[2]
ζ1 UMa
Right ascension 13h 23m 55.543s[3]
Declination +54° 55′ 31.30″[3]
Apparent magnitude (V) 2.23[3]
ζ2 UMa
Right ascension 13h 23m 56.330s[3]
Declination +54° 55′ 18.56″[3]
Apparent magnitude (V) 3.88[3]
Characteristics
ζ1 UMa
Spectral type A2Vp/A2Vp[4]
U−B color index −0.01[5]
B−V color index +0.02[5]
ζ2 UMa
Spectral type kA1h(eA)mA7IV-V[6]
U−B color index +0.09[5]
B−V color index +0.13[5]
Astrometry
Radial velocity (Rv)−6.31[7] km/s
Proper motion (μ) RA: 119.01[1] mas/yr
Dec.: −25.97[1] mas/yr
Parallax (π)39.36 ± 0.30 mas[8]
Distance82.9 ± 0.6 ly
(25.4 ± 0.2 pc)
Absolute magnitude (MV)+0.32/+1.96[9]
Orbit
PrimaryMizar Aa
CompanionMizar Ab
Period (P)20.5386 days[10]
Semi-major axis (a)9.83±0.03[11] mas
Eccentricity (e)0.5415±0.0016[10]
Inclination (i)60.5±0.3[10]°
Longitude of the node (Ω)106.0±0.4[11]°
Periastron epoch (T)RJD 54536.9904[10]
Argument of periastron (ω)
(secondary)		105.27±0.23[10]°
Semi-amplitude (K1)
(primary)		66.478±0.153[10] km/s
Semi-amplitude (K2)
(secondary)		66.019±0.177[10] km/s
Orbit
PrimaryMizar Ba
CompanionMizar Bb
Period (P)175.55 d[12]
Semi-major axis (a)29.849 mas
Eccentricity (e)0.46[12]
Details
Mizar Aa
Mass2.2224±0.0221[10] M☉
Radius2.4 ± 0.1[11] R☉
Luminosity33.3 ± 2.1[11] L☉
Temperature9,000 ± 200[11] K
Age370[13] Myr
Mizar Ab
Mass2.2381±0.0219[10] M☉
Radius2.4 ± 0.1[11] R☉
Luminosity33.3 ± 2.1[11] L☉
Temperature9,000 ± 200[11] K
ζ2 UMa
Surface gravity (log g)4.40[14] cgs
Temperature8,425[14] K
Rotational velocity (v sin i)61[14] km/s
Other designations
ζ Ursae Majoris, ζ UMa, Zeta UMa, 79 Ursae Majoris, BD+55 1598, CCDM J13240+5456, HIP 65378, WDS J13239+5456
ζ1 UMa: GC 18133, HD 116656, HR 5054, PPM 34007, SAO 28737
ζ2 UMa: GC 18134, HD 116657, HR 5055, SAO 28738
Database references
SIMBADMizar
ζ1 UMa
ζ2 UMa

Mizar /ˈmaɪzɑːr/[15] 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.

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  15. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.