Mimas (from the Greek "Μίμᾱς") is one of Saturn's largest moons. It is also called Saturn I. Mimas is best known for its large crater, Herschel. In the centre of the crater is a very high mountain. Mimas was discovered by the English astronomer William Herschel on September 17, 1789. The moon is believed to have created the Cassini Division. This is a 4,800 km gap between Saturn's A and B rings.