Butterfly star cluster. True-colour optical image of the open star cluster M6 (NGC 6405), also known as the Butterfly cluster, which lies in the constellation Scorpius. The Butterfly cluster is one of the largest and brightest open star clusters, being formed of over 130 stars having a combined magnitude of 4. The stars are thought to be around 100 million years old. The cluster is about 20 light years across, and is thought to be 1400 light years from Earth. This image was produced by digitally combining photographs taken by the UK Schmidt Telescope in blue and red light.