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Mizar and Alcor form a naked eye double star in the handle of the Big Dipper asterism in the constellation Ursa Major. Mizar is itself a quadruple system and Alcor is a binary, the pair together forming a sextuple system. == Description == Mizar (Zeta Ursae Majoris, Zeta UMa, ζ Ursae Majoris, ζ UMa, known as Arundhati-Vasishtha in Sanskrit (अरुन्धती-वसिष्ठ) and in Arabic as "" (''mīzar'', meaning a waistband or girdle) is a quadruple system, a visual double with a separation of 14.4 arcseconds, each of which is a spectroscopic binary, in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23 and its spectral class is A2V. With normal eyesight one can make out a faint companion just to the east, about 12 minutes of arc from Mizar, named Alcor or 80 Ursae Majoris. Alcor is of magnitude 3.99 and spectral class A5V. It has a faint red dwarf companion separated by 1". Mizar and Alcor's proper motions show they move together (they are both members of the Ursa Major Moving Group), but it has yet to be demonstrated conclusively that they are gravitationally bound. Recent studies indicate that the Alcor binary and Mizar quadruple are somewhat closer together than previously thought: approximately 74,000 ± 39,000 astronomical units or 0.5–1.5 light years. The whole six-star system lies about 83 light-years away from Earth, as measured by the Hipparcos astrometry satellite. The components are all members of the Ursa Major moving group, a mostly dispersed group of stars sharing a common birth, as determined by proper motion. The other stars of the Big Dipper, except Dubhe and Alkaid, belong to this group as well. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mizar and Alcor」の詳細全文を読む スポンサード リンク
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