Along with Andromeda, Cassiopeia, Cepheus, and Pegasus, Perseus is involved in one of the oldest stories in history and is one of the most ancient constellations. Perseus was a mortal son of the god Zeus. He was destined for a life of adventure and after being armed with mystical weapons made by the gods encountered his destiny. He first slew the Gorgon, Medusa, and then rescued the princess Andromeda from being sacrificed to the sea monster Cetus. The constellation of Perseus can be found southeast of Cassiopeia. Within the constellation is the star Algol, the "demon star". Algol is variable star which changes its brightness every 2.87 days. To the ancients this star was the head of Medusa, who even after death winked at them.