Chi Persei open star cluster. True-colour optical image of the open star cluster Chi Persei (NGC 884). This is one of a pair of star clusters which form the Double Cluster in the constellation Perseus. The two star clusters, about 7000 light years from Earth, are named after their brightest members. This cluster, and its twin NGC 869 (out of frame at right), are approximately the same age (10-20 million years old), and lie about 50 light years apart. They are thought to have formed from a large cloud of gas which broke into two before condensing into stars. This image was produced by digitally combining photographs taken by the Palomar Schmidt Telescope in blue and red light.