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Omega Centauri (ω Cen), or NGC 5139, is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 15,800 light-years (4,850 pc), it is the largest globular cluster in the Milky Way galaxy at a diameter of roughly 150 light-years.〔(【引用サイトリンク】url=http://www.universeforfacts.com/2013/11/omega-centauri-largest-globular-cluster.html )〕 It is estimated to contain approximately 10 million stars and a total mass equivalent to 4 million solar masses.〔http://apod.nasa.gov/apod/ap100331.html〕 Omega Centauri is so distinctive from the other galactic globular clusters that it is thought to have an alternate origin as the core remnant of a disrupted dwarf galaxy.〔 ==Observation history== In 150 A.D., Greco-Roman writer and astronomer Ptolemy catalogued this object in his ''Almagest'' as a star on the horse's back, "Quae est in principio scapulae". German lawyer and cartographer Johann Bayer used Ptolemy's data to designate this object "Omega Centauri" with his 1603 publication of ''Uranometria''. Using a telescope from the South Atlantic island of Saint Helena, English astronomer Edmond Halley rediscovered this object in 1677, listing it as a non-stellar object. In 1715, it was published by Halley among his list of six "luminous spots or patches" in the ''Philosophical Transactions of the Royal Society''.〔 Swiss astronomer Jean-Philippe de Cheseaux included Omega Centauri in his 1746 list of 21 nebulae,〔 as did French astronomer Lacaille in 1755, who gave it the catalogue number L I.5. It was first recognized as a globular cluster by Scottish astronomer James Dunlop in 1826, who described it as a "beautiful globe of stars very gradually and moderately compressed to the centre".〔〔 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「Omega Centauri」の詳細全文を読む スポンサード リンク
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