Cepheus was one of the original 48 constellations cataloged by the Second Century Greek astronomer Ptolemy, and is still one of 88 officially recognized modern constellations. It sits on the south side of the sky in the Northern Hemisphere, near Cassiopeia, Cygnus, and Lacerta.
In all, the constellation contains 43 known stars, seven of which make up its shape, a box with a triangle on top, said to represent a seated king. Some of its more interesting stars include Delta Cephei, a variable star that grows brighter and darker in cycles of about five days, Gamma Cephei, also known as Errai, which is actually a binary star system (two stars revolving around one another), and three red supergiants, Mu Cephei, also known as the Garnet Star, VV Cephei, and V381 Cephei. These last three are among the largest known stars in the Universe.
Cepheus does not contain any Messier objects, bright deep sky objects identified primarily by French astronomer Charles Messier during the 18th Century. It does, however, contain three other objects of note listed in the New General Catalogue: NGC 6946, also known as the Fireworks Galaxy, a spiral galaxy where astronomers have observed an unparalleled nine supernovae; NGC 7538, a nebula that is home to the largest known protostar (a star in the process of forming); and NGC 188, one of the oldest known open clusters.
Cepheus takes its name from Greek mythology. King Cepheus was a legendary king of Ethiopia, husband of Cassiopeia, whose constellation sits next to his in the sky, and father of Andromeda. Cepheus is not a very exciting figure. He is immortalized in the sky more for the actions of those closest to him than for anything he himself did. His wife, Cassiopeia, became famous for being so vain and boastful about her beauty that she claimed to be even more beautiful than the Nereids, the daughters of the sea-god Poseidon. To punish Cassiopeia for her vanity, Poseidon chained Andromeda to a rock to be devoured by a sea monster.
That’s where the hero Perseus entered the scene. Cepheus told Perseus, who had already proven himself by taking the head of the snake-headed monster Medusa, that if he saved Andromeda from the monster, he would win the right to marry her. Perseus fought off the monster and was set to wed the girl. During the wedding, however, Perseus learned that Andromeda had already been promised to another man, Cepheus’ own brother Phineus (eww!).
Once his daughter was safe and sound, Cephus forgot his promise to Perseus and sided with Phineus. A great battle ensued between Perseus on one side and the supporters of Phineus on the other. Outnumbered, Perseus used a very special weapon to overcome his enemies. He removed the head of Medusa from the bag where he kept it, and her magical gaze instantly turned all who entered it into stone. This is how Cepheus and Cassiopeia perished. Perhaps as a reminder to humanity of the fruits of vanity and broken promises, the king and queen were immortalized in the stars by the gods for all eternity.