The solar system consists of the Sun and objects that orbit it, including eight planets, over 200 moons, and millions of asteroids, comets and meteoroids. It is located within the Milky Way galaxy, which contains hundreds of billions of stars. The Earth has one natural satellite, the Moon, and revolves around the Sun while also rotating on its axis. It is composed of three main layers - the atmosphere, hydrosphere and geosphere. The Moon orbits Earth and has different phases as it rotates and revolves, presenting different illuminated portions to observers over the course of a month.