Concept

Mizar

Summary
Mizar 'maizɑr 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. ζ Ursae Majoris (Latinised to Zeta Ursae Majoris and abbreviated to ζ UMa or Zeta UMa) is Mizar's Bayer designation. It also has the Flamsteed designation 79 Ursae Majoris. The traditional name Mizar derives from the Arabic ALA meaning 'apron; wrapper, covering, cover'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Mizar for ζ UMa. According to IAU rules, the name Mizar strictly only applies to component Aa, although it is traditionally and popularly used for all four stars making up the single naked-eye star. Mizar is a visual double with a separation of 14.4 arcseconds, each of which is a spectroscopic binary. Its combined apparent magnitude is 2.04. The two visible stars are referred to as ζ1 and ζ2 Ursae Majoris, or Mizar A and B. The spectroscopic components are generally referred to as Mizar Aa, Ab, Ba, and Bb. The stars all share a single Hipparcos designation of HIP 65378, but separate Bright Star Catalogue and Henry Draper Catalogue entries. Mizar, together with Alcor and many of the other bright stars in Ursa Major, is a member of the Ursa Major Moving Group. An easily split visual target, Mizar was the first telescopic binary discovered, most probably by Benedetto Castelli who in 1617 asked Galileo Galilei to observe it. Galileo then produced a detailed record of the double star. Later, around 1650, Riccioli wrote of Mizar appearing as a double.
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