Chapter 1: a modern view of the universe. The old belief was in a geocentric universe where everything revolved around the. Earth is a planet in our solar system, which consists of the sun, the planets and their moons, and countless smaller objects (i. e. rocky asteroids, icy comets). Our solar system is part of the milky way galaxy, which has +100b stars. Galaxy: a great island of stars in space, containing from a few hundred million to a trillion or more stars, all held together by gravity and orbiting a common centre. Local group: group of more than 40 galaxies, including the milky way (one of the two largest member galaxies). Galaxy cluster: a collection of galaxies bound together by gravity: small collections (up to a few dozen galaxies) groups, large collections clusters. Supercluster: a gigantic region of space in which many groups/clusters of galaxies are packed more closely together than elsewhere in the universe.