What is a Galaxy?

Earth is our home planet. It orbits the Sun together with the other eight planets, comets, asteroids and all of the other stuff that makes up the Solar System. But where is the Solar System located? It turns out that the Solar System is part of a much larger structure, called a galaxy. The Sun is a star, just like the others you see when you look up on a clear night. They are very far away from us and therefore look dim compared to the Sun. All of these Stars are all part of the same galaxy. That galaxy is called the Milky Way. A galaxy is a very large group of stars, dust, gas and dark mater that is gravitationaly bound together. A galaxy can range in size from a few hundred million stars up to large galaxyies containing 100 trillion stars.