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Messier 12 or M 12 (also designated NGC 6218) is a globular cluster in the constellation of Ophiuchus. It was discovered by the French astronomer Charles Messier on May 30, 1764, who described it as a "nebula without stars".〔 In dark conditions this cluster can be faintly seen with a pair of binoculars. Resolving the stellar components requires a telescope with an aperture of or greater.〔 In a scope, the granular core shows a diameter of 3′ (arcminutes) surrounded by a 10′ halo of stars.〔 Located roughly 3°〔 in the sky from the cluster M10 and 5.6° from the star Lambda Ophiuchi, M12 is about 〔 from Earth and has a spatial diameter of about 75 light-years. The brightest stars of M12 are of 12th magnitude. With a Shapley-Sawyer rating of IX,〔 it is rather loosely packed for a globular and was once thought to be a tightly concentrated open cluster. Thirteen variable stars have been recorded in this cluster. M12 is approaching us at a velocity of 16 km/s. A study published in 2006 concluded that this cluster has an unusually low number of low mass stars. The authors surmise that they were stripped from the cluster by the gravitational influence of the Milky Way.〔 Image:Messier12.jpg|Messier 12, from ''2MASS'' Image:M12HunterWilson.jpg|M12 with amateur telescope Image:ESO-Messier 12-Phot-04a-06.jpg| The Central Part of Messier 12. Credit: ESO Image:M12map.png|Map showing the location of M12. Credit: Roberto Mura. ==Notes== 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「Messier 12」の詳細全文を読む スポンサード リンク
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