There is an uncountable number of galaxies made up of stars. Our galaxy, the Milky Way, is 10,000 light years big and contains between 2 and 4 thousand million stars. The solar system orbits the sun and contains 8 planets, some of which have moons. The largest moons in our solar system include Ganymedes, Titan, Callisto, Io, Earth's moon, Europe, and Triton.