Pleiades star cluster (M45). This cluster contains around 500 stars that all formed from the same cloud of gas around 100 million year ago, very recently in stellar terms. A blue reflection nebula surrounds the stars, which shines by reflecting their light. The nebula is not associated with the history of the cluster, instead the stars are just happening to move through a dusty region of space. The Pleiades is one of the nearest star clusters to Earth, at around 440 light years distant. In excellent observing conditions, as many as 14 of the stars can be seen with the naked eye. Photographed by the 1.22-metre Oschin Telescope at Mount Palomar, California, USA.