Hoag's Object, an unusual ring-shaped galaxy. The galaxy appears to comprise a central nucleus completely cut off from its disc by a band of empty space. As with conventional spiral galaxies, the disc appears blue as it contains mainly hot young blue stars, while the nucleus, containing older stars and dust, appears yellower. Although the details of its formation are not known, it is thought that the ring may be the remains of another galaxy that was torn apart by gravitational interaction with the central galaxy. It lies 600 million light years from Earth in the constellation Serpens. Image taken by the Wide Field and Planetary Camera 2 on the Hubble Space Telescope on 9th July 2001.