Each galaxy has billions of stars. Such galaxies are not uniformly spaced in the universe but exist in groups and clusters; a group containing up to 40-50 galaxies and clusters containing about thousands of galaxies. These along with isolated galaxies may form larger clusters known as galactic superclusters. These are the largest structures of matter found in the universe. Our galaxy, the Milky Way, is a member of a local group of galaxies, which is in turn a part of the Virgo supercluster.