Just as Helios personified the sun, so his sister Selene represented the moon, and was supposed to drive her chariot across the sky whilst her brother was reposing after the toils of the day.
When the shades of evening began to enfold the earth, the two milk-white steeds of Selene rose out of the mysterious depths of Oceanus.
Seated in a silvery chariot, and accompanied by her daughter Herse, the goddess of the dew, appeared the mild and gentle queen of the night, with a crescent on her fair brow, a gauzy veil flowing behind, and a lighted torch in her hand. Selene greatly admired a beautiful young shepherd named Endymion, to whom Zeus had accorded the privilege of eternal youth, combined with the faculty of sleeping whenever he desired, and as long as he wished. Seeing this lovely youth fast asleep on Mount Latmus, Selene was so struck with his beauty, that she came down every night from heaven to watch over and protect him.
From: Berens, E.M. The Myths and Legends of Ancient Greece and Rome. New York: Maynard, Merril, & Co., 1880. Text in the public domain.