The Pleiades
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	Common Name: The Pleiades Other Names: M45, The Seven Sisters, Subaru, Soraya, The Clusterers. RA: 03 : 47.0 Dec +24 : 07 Constellation: Taurus Distance: 440 light years Magnitude: 1.6 Telescope: Meade LX200GPS 14" Camera: SBig ST-8 Filters: RGB Exposure: Date: 2007 Software acquisition: acquired with ccdsoft Processing Software: Maxim DL, stacking, color combine, stretch 0.2, exp histogram. Where: Tenby Observatory, Coonabarabran Lat: 31 16 35.05 S, Long 149 11 33.99 E, Elevation 547metres Notes: The Pleiades is an open cluster of stars situated on the shoulder of the constellation Taurus. To the naked eye the number of stars visible varies depending on the seeing conditions but generally 7 can be seen. On exceptional nights I have seen 9 with averted vision. Though as many as 14 have been recorded in their correct positions before the telescope was invented. Must have been no light pollution then. The actual number is around 500 stars spanning an area 4 times the size of the moon. The brightest stars are Alcyone ( magnitude 2.84), Atlas ( 3.59), Electra (3.71), Maia (3.84), Merope (4.12), Taygeta (4.28), Pleione (4.77 - 5.5), Calaeno (5.43), Asterope (5.75). and are are named after the daughters of Atlas and Pleione. Some of these stars are rapidly rotating. So fast in fact they are not round but are egg shapped. This can be deduced from obseving their spectral lines which have broadened by the doppler affect. Pleione has ejected 3 shells of gas in the last 100 years because of the rapid rotation. The group of stars was recognised to be an open cluster in 1846 by the astronomer Madler. He found the stars had the same proper motion across the sky. The age of the cluster is about 100 million years. The cluster originated in Gould's belt . As with all open clusters they form from a nebula of hydrogen gas and dust. The solar wind from the stars blows away the gas and dust and an open cluster of stars results. Over time the stars will drift apart from each other and become indivdual stars. This will happen in about 250 million years for the Pleiades. The photograph above shows nebulosity and appears to be a reflection nebula as its a blue colour. This nebulae is called Tempel's Nebula or the Merope Nebula and also NGC 1435. This nebula is not part of the star cluster at all but is closer to us. It has a different proper motion across the sky. Several white dwarf stars have been observed which is a mystery. The cluster is not old enough for its stars to evolve to this stage. There is time for the most massive stars to evolve and die but these normally produce neutron stars or black holes. This can only mean either the white dwarfs formed separately from the cluster or there is another mechanism how white dwarfs can form. Perhaps very massive stars lose a lot of mass from their rapid rotation.