The Pleiades (The Seven Sisters)

The Pleiades (Messier Object 45) has a very unique feature in astronomy. It is the most obvious star cluster to the naked eye in the night sky; along with being one of the closest star clusters. This cluster is found at the shoulder of the bull in the constellation Taurus. The Pleiades were used by the ancient Greek sailors as a type of weather forecast: if the Pleiades were visible it was a good time to set sail; if the Pleiades were not visible, most likely a storm was coming. The conjunction of the cluster with the sun in the spring signified the beginning of the summer sailing season, while the opposition in the fall signified the end of the sailing season.

The Pleiades star cluster consists of over 400 mostly faint stars, along with the 6 to 15 brighter stars seen well with the naked eye during good viewing conditions. There are also several nebulae within the star cluster. These nebulae are blue in color indicating reflection nebulae, which reflect the light of bright stars near or within the nebulae. The reflection nebula seen at right is most likely part of the dust in a molecular cloud and is not actually related to the Pleiades; these two bodies are simply crossing each other in the sky, like two ships in the night. It is estimated that the Pleiades star cluster will survive for roughly another 250 million years. Gravitational interactions with the spiral arms of the galaxy and giant molecular clouds will cause the demise of this most impressive star cluster.

The Seven Sisters are the daughters of the titan Atlas, who held up the sky, and the sea-nymph Pleione, the protectress of sailing. The daughters were Maia (the eldest), Electra, Taygete, Alcyone, Celaeno, Sterope (which is a double star) and Merope (the youngest). Their half-sisters include the Hyades, Calypso, Hyas and the Hesperides.

The only one of the seven sisters to marry a mortal was Merope, who wed Sisyphus and bore him several sons. The other six sisters all consorted with gods. Zeus sired four children with three of the sisters. Poseidon was father to three children from two of the sisters and Ares fathered a child with one sister.

Atlas joined one of his brothers and several other Titans in a war against the Olympic gods. Two of Atlas’ brothers, after weighing the odds, betrayed the battling Titans by siding with the Olympians. The Titans were defeated and Zeus condemned Atlas to stand at the edge of the Earth and hold up the heavens with his shoulders.

One day while strolling the Boeotian countryside, the Pleiades were spotted by Orion, the great hunter. Orion was immediately taken by the incredible beauty of the seven sisters and pursued them across the earth for seven years. Zeus took pity on the sisters on behalf of Orion’s relentless pursuit of them and changed them into doves, giving them a place in the heavens and putting them again under their father’s watchful eye. When Orion was later placed in the heavens, he was set in a position to be behind the Pleiades, forever chasing the lovely ladies he couldn’t catch while mortal.

For more on the world of astronomy, visit Starr’s site at Space for the Earthbound