Pleiades (star cluster)

The Pleiades (also known as M45 or the Seven Sisters) is an open cluster in the constellation of Taurus. It is among the nearest to earth of all open clusters, probably the best known and certainly the most striking to the naked eye.

History

The Pleiades are a prominent sight in the northern hemisphere in winter, and have been known since antiquity to cultures all around the world, including the Maori and Australian Aborigines, the Japanese and the Sioux of North America. Some Greek astronomers considered them to be their own constellation, and they are mentioned in Homer's Iliad and Odyssey, and also by Hesiod. They are also mentioned three times in the Bible (Job 9:9, 38:31; Amos 5:8).

Related Topics:
Northern hemisphere - Winter - Maori - Australian Aborigine - Japanese - Sioux - North America - Greek - Constellation - Homer - Iliad - Odyssey - Hesiod - Bible

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They have long been known to be a physically related group of stars rather than any chance alignment. The Reverend John Michell calculated in 1767 that the probability of a chance alignment of so many bright stars was only 1 in 500,000, and so correctly surmised that the Pleiades and many other clusters of stars must be physically related {{ref|Michell}}. When studies were first made of the stars' proper motions, it was found that they are all moving in the same direction across the sky, at the same rate, furthering demonstrating that they were related.

Related Topics:
John Michell - 1767 - Proper motion

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Charles Messier measured the position of the cluster and included it as M45 in his catalogue of comet-like objects, published in 1771. Along with the Orion Nebula and the Praesepe cluster, Messier's inclusion of the Pleiades has been noted as curious{{ref|Messier}}, as most of Messier's objects were much fainter and more easily confused with comets—something which seems scarcely possible for the Pleiades. One possibility is that Messier simply wanted to have a larger catalogue than his scientific rival Lacaille, whose 1755 catalogue contained 42 objects, and so he added some bright, well-known objects to boost his list.

Related Topics:
Charles Messier - Catalogue - Comet - 1771 - Orion Nebula - Praesepe - Lacaille - 1755

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