1 Greek Mythology a Titaness, daughter of Uranus (Heaven) and Gaia (Earth). She became the mother of Leto and thus the grandmother of Apollo and Artemis. In the later Greek writers, her name was often used for Selene (Moon). 2 Astronomy a satellite of Saturn, the furthest from the planet and with an eccentric retrograde orbit, discovered in 1898. At a distance of 8 million miles (13 million km) from Saturn, it has a diameter of 137 miles (220 km).