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Zeta1,2 Ursae Majoris, 79 Ursae Majoris

Proper NameMizar
Bayer DesignationZeta1 Ursae Majoris (A)
Zeta2 Ursae Majoris (B)
Flamsteed Number79 Ursae Majoris
HR (BSC)5054 (A), 5055 (B)
HD116656 (A), 116657 (B)
ConstellationUrsa Major
Right Ascension13h 23m 56s (A), 13h 23m 56s (B)
Declination+54° 55' 31" (A), +54° 55' 19" (B)
Distance81 light years
25 parsecs
MagnitudeApparent: +2.2 (A), +3.9 (B)
Absolute: +0.2 (A), +1.9 (B)
Spectral ClassA1VpSrSi white main sequence star (A)
A1IV white subgiant (B)
Optimum VisibilityApril / May (Usually visible from northern latitudes)
NotesMizar is historically important as being the first binary star to be identified. Its double nature was established in 1650, but it is now known to be quadruple system, with both Mizar A and Mizar B being spectroscopic binaries (that is, systems in which the binary companion is not directly visible, but is revealed by movements in the star's spectral patterns).

Mizar is one of the seven prominent stars that form the asterism known as the Plough (or Big Dipper) in the constellation of Ursa Major, the Great Bear. Mizar is the middle star of the three that make up the 'handle' of the Plough, and is a quadruple system, consisting of two binary pairs. It is closely associated with the fainter Alcor (indeed, Mizar and Alcor are together sometimes called the 'Horse and Rider'). Alcor is itself a binary, which is thought likely to form an outlying member of the Mizar system a little over a light year away from the other four stars, and thus Mizar and Alcor together form a loose sextuple star system.


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