Solar system- a star and all of the objects that orbit around it. The planets and their moons as well as asteroids and around the sun. comets orbiting. Galaxy- a great island of stars in space, containing from a few hundred million to a trillion or more stars bound together by gravity. Milk way galaxy- huge, disk-shaped collection of more then 100 million stars. Local group- the group of approximately 40 galaxies to which milky. Cluster of galaxies- a collection of a few dozen or more galaxies bound together by gravity. Group of galaxies- a few to a dozen galaxies bound together by gravity. Supercluster- the region in which galaxies and galaxy clusters are most tightly packed. (clusters of galaxy clusters) Universe- the sum total of all matter and energy, encompassing the superclusters and voids and everything within them. The big bang is the point when expansion began, 14 million years ago.