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Pleiades
In astronomy, the Pleiades ( or ), or Seven Sisters (Messier 45 or M45), is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky. The celestial entity has several meanings in different cultures and traditions.
The cluster is dominated by hot blue and extremely luminous stars that have formed within the last 100 million years. Dust that forms a faint reflection nebulosity around the brightest stars was thought at first to be left over from the formation of the cluster (hence the alternative name Maia Nebula after the star Maia), but is now known to be an unrelated dust cloud in the interstellar medium, through which the stars are currently passing. Computer simulations have shown that the Pleiades was probably formed from a compact configuration that resembled the Orion Nebula. Astronomers estimate that the cluster will survive for about another 250 million years, after which it will disperse due to gravitational interactions with its galactic neighborhood.
==Origin of name==
The name of the Pleiades comes from Ancient Greek. It probably derives from ''plein'' ('to sail') because of the cluster's importance in delimiting the sailing season in the Mediterranean Sea: 'the season of navigation began with their heliacal rising'.〔"Pleiad, n." OED Online. Oxford University Press, December 2014. Web. 20 January 2015.〕 However, the name was later mythologised as the name of seven divine sisters, whose name was imagined to derive from that of their mother Pleione, effectively meaning 'daughters of Pleione'. However, in reality the name of the star-cluster almost certainly came first, and Pleione was invented to explain it.〔Robin Hard, ''The Routledge Handbook of Greek Mythology'' (London: Routledge, 2004), p. 518.〕
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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