Cassiopeia

Cassiopeia is a constellation in the northern sky. It was one of the 48 constellations listed by the 2nd century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today. Cassiopeia is easily recognizable due to its distinctive 'W' shape formed by five bright stars. Cassiopeia A was first seen in 1680. In the sky Cassiopeia sits with Andromeda on the South side, Perseus on the South East and Cepheus to the North. She is opposite The Big Dipper, and can be seen the clearest in early November. In Greek mythology it was considered to represent the vain queen Cassiopeia, who boasted about her unrivaled beauty.

Within Cassiopeia’s five major stars lies Cassiopeia A; commonly referred to as Cas A. Cas A is the remnant of supernova Tycho which exploded in late 1572. Cassiopeia A is approximately 300 years old and has the distinction of being the strongest radio source observable outside our solar system. Its first viewing was in 1680 by John Flamsteed and was appropriately named Cassiopeia A because it is within the boundary of the constellation. It was the first image brought back by the Chandra x-ray observation In the late 1990’s. Similar to Cas A there are other stars and supernova remnants referred to as Cassiopeia B,T etc, and may be located in the larger constellation, though they too are only small parts of the whole.

Cassiopeia contains two stars visible to the naked eye that rank among the most luminous in the galaxy: ρ Cas and V509 Cas. The star η Cas is a nearby (19.4 ly) binary star comprising a yellow Sun-like dwarf and an orange dwarf star.

Mythology

Cassiopeia’s story originated in the mythology of ancient Greece. Cassiopeia was the queen and consort of King Cepheus in Ethiopia. Their daughter Andromeda was very beautiful. Cassiopeia herself was a great beauty and was vain of it; she proclaimed her beauty was greater than that of the Nereids', the daughters of the sea god Poseidon. To punish Cassiopeia, he sentenced Andromeda to be tied to a rock with a sea monster awaiting her.

Perseus, returning from having slaughtered the gorgon Medusa, encountered the body of Andromeda lashed to the rock. He spoke to Cassiopeia and her husband and struck a deal with them: he would be allowed to marry Andromeda if he could kill the great sea monster before it killed their virgin daughter (who had been betrothed to her uncle Phineus). Perseus defeated the monster, took Andromeda and returned to Ethiopia. Cassiopeia and Cepheus fulfilled their end of the bargain and began to plan the wedding for Andromeda. After the nuptials began, Phineus entered the proceedings and demanded his right to marry Andromeda.

A battle ensued in which Cepheus and Cassiopeia sided with Phineus. Outnumbered, Perseus considered that he had no choice but to slay his challengers by using the head of the recently slaughtered Medusa. Following their death both Cepheus and Cassiopeia were placed among the stars by Poseidon. Cassiopeia was put upside down for half the year because of her vanity, with her husband beside her.