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Alnitak
Alnitak ((アラビア語:النطاق ''an-niṭāq'')) is a multiple star several hundred parsecs away in the constellation Orion. It is part of Orion's Belt along with Alnilam and Mintaka, and has a Bayer designation of Zeta Orionis (ζ Ori) and a Flamsteed designation of 50 Orionis.
The primary star is a hot blue supergiant with an absolute magnitude of -6.0 and is the brightest class O star in the night sky with a visual magnitude of +2.0. It has two bluish 4th magnitude companions, one finely resolved and one only detected interferometrically and spectroscopically, producing a combined magnitude for the trio of +1.77. The stars are members of the Orion OB1 association and the Collinder 70 association.
==Observation history==
Alnitak has been known since antiquity and, as a component of Orion's belt, has been of widespread cultural significance. It was reported to be a double star by amateur German astronomer George K. Kunowsky in 1819.〔 Much more recently, in 1998, the bright primary was found by a team from the Lowell Observatory to have a close companion; this had been suspected from observations made with the Narrabri Stellar Intensity Interferometer in the 1970s.〔 The stellar parallax derived from observations by the Hipparcos satellite imply a distance around 225pc, but this does not take into account distortions caused by the multiple nature of the system and larger distances have been derived by many authors.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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