A prominently located constellation in the northern sky (see illustration), named for the daughter of Cassiopeia in Greek mythology: When Cassiopeia bragged that her daughter Andromeda was more beautiful than Poseidon's daughters, the Nereids, Poseidon created Cetus, the sea monster. (In some versions of the myth, Cassiopeia boasted of her own beauty.) The situation required Andromeda's sacrifice. However, Perseus saved Andromeda by showing Cetus the head of Medusa, turning Cetus to stone.