Mizar and Alcor

Common card · No. 363527

Mizar and Alcor are two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in the constellation of Ursa Major. Their magnitudes are 2.2 and 3.9, and the pair can easily be seen without the aid of a telescope. Mizar and its fainter companion Alcor are actually a senary system consisting of two pairs of double stars, one of which is itself a double binary system. The six stars are gravitationally bound to each other. The traditional name Mizar derives from the Arabic المئزر or mi'zar, meaning 'apron; wrapper, cover'. Alcor was originally the Arabic سها or suhā/sohā, meaning either 'the forgotten' or 'neglected one'. The Arabs and the ancient Persians used distinguishing Mizar and Alcor as a test of vision. Mizar, also designated Zeta Ursae Majoris (ζ Ursae Majoris, abbreviated Zeta UMa, ζ UMa), is itself a quadruple system and Alcor, also designated 80 Ursae Majoris (80 UMa), is a binary star, the pair together forming a sextuple system. Mizar was the first...

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