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NGC 6231 , also known as the Northern Jewel Box, is an open cluster located near Zeta Scorpii. Zeta1 (HR 6262) is a member of this star cluster. (Its brighter apparent partner, Zeta2 (HR 6271), is only 150 ly from Earth and so is not a cluster member.) This cluster is estimated about 3.2 million years old, and is approaching the Solar System at 22 km/s. The cluster belongs to the young Scorpius OB1 association. Zeta1 Scorpii (spectral type O8 and magnitude 4.71.〔''Sky Catalogue 2000.0''〕) is the brightest star in the association, and one of the most radiant stars known in the galaxy.〔Crossen & Tirion, ''Binocular Astronomy'', p. 119.〕 NGC 6231 also includes three Wolf-Rayet stars: HD 151932, HD 152270,〔(Study of the Wolf-Rayet members of the cluster NGC 6231 )〕 and HD 152408.〔(The distinction between OIafpe and WNLha stars. A spectral analysis of HD 151804, HD 152408 and HDE 313846. )〕 The cluster was discovered by Giovanni Batista Hodierna before 1654. Hodierna listed it as ''Luminosae''〔Stars visible to the naked eye. It meanings "luminous" in Latin.〕 in his catalogue of deep sky observations. This catalogue was included in his book ''De Admirandis Coeli Characteribuse'' published in 1654 at Palermo. It was independently observed by other astronomers after Hodierna. : * 1678 Edmond Halley : * 1745-46 de Chéseaux : * 1751-52 Lacaille The cluster forms the head of the "false comet", the tail being the dimmer cluster Trumpler 24 extending to the north, also part of the Scorpius OB1 association. ==See also== * New General Catalogue 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「NGC 6231」の詳細全文を読む スポンサード リンク
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