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Mizar, Zeta Ursae Majoris

Multiple star system in Ursa Major

Right Ascension 13 : 23 : 55.5 (h:m:s)
Declination +54 : 55 : 31 (deg:m:s)
Distance 76 (ly)
Visual brightness 2.27 (mag)
Spectral type A1V p SrSi

Discovered as double star by Benedetto Castelli on February 4, 1617.
Independently found by Giovanni Battista Riccioli around 1650.

The multiple star system zeta UMa (called Mizar - from the arabian word for girdle) belongs to the most famous multiple stars in the sky. It's brightness is about 2.4 mag; therefore under very good conditions it is possible for the naked eye to see the 4th mag. companion, called 'Alcor' or 80 UMa (otherwise a small binocular will help). In small telescops another 4th mag star becomes visible. Each of these stars is as well a spectroscopic binary.

The Mizar system is a member of the nearby Ursa Major Moving Cluster (Collinder 285)


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