DescriptionMizar 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 four-star binary system consisting of two pairs of double stars that 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 ancient Persians and the Bedouins 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 known binary star system, claimed to be discovered by Italian astronomer Giovanni Battista Riccioli in 1650. The whole system lies about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite.With normal eyesight Alcor appears at about 12 arcminutes from Mizar. Alcor is of magnitude 3.99 and spectral class A5V. It has a faint red dwarf companion separated by 1 arcsecond. Mizar and Alcor's proper motions show they move together, along with most of the other stars of the Big Dipper except Alpha Ursae Majoris and Eta Ursae Majoris, as members of the Ursa Major moving group, a mostly dispersed group of stars sharing a common birth. However, it has yet to be demonstrated conclusively that they are gravitationally bound. Parallax measurements by Gaia indicate that Alcor and Mizar are somewhat closer together than previously thought: 0.36±0.19 pc. The uncertainty is due to not knowing exactly how far away the stars are. If they are exactly the same distance from us then the distance between them is only 17800 AU (0.281 ly). Between Mizar and Alcor, the 8th-magnitude star Sidus Ludoviciana is a distant background object.Alcor Star is located on lower left and Mizar Star is located on upper center.

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