The Pleiades or Messier 45 are an example of an open star cluster, a group of stars that were all born around the same time from a gigantic cloud of gas and dust. They are one of the most easily recognisable star patterns (sometimes known as an asterism) in the night sky, although whoever gave them their popular name of the 'Seven Sisters' clearly couldn't count! When you look at a photograph it's hard to discern which seven stars were originally the ones from which the name derives.
There are more than 800 middle-aged, hot B-type stars in the group which lies in the north-west of the constellation Taurus. Te hey are located about 440 light-years from Earth and are approximately 17.5 light years wide. The brightest stars in the cluster glow a hot blue and formed within the last 100 million years. They are extremely luminous and will burn out quickly, with life spans of only a few hundred million years, much shorter than the billions of years our own sun.
The name 'Seven Sisters' is derived from Greek legend. The Pleiades are the seven daughters of the Titan god Atlas and the ocean nymph Pleione. During an ancient war, Atlas rebelled against Zeus, the king of the gods, who sentenced his foe to forever hold up the heavens on his shoulders. The sisters were so sad that Zeus allowed them a place in the sky in order to be close to their father.
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