Spanning nearly 200 light-years, IC 1805—known colloquially as the heart nebula—is a stellar nursery in which we find the star cluster Melotte 15. Compared to our own 5 billion year-old Sun, the stars of Melotte 15 are still in their infancy at a mere 1.5 million years of age. Destined to live short lives and violent deaths, the stars of the cluster are ionizing the hydrogen gas from which they formed and it is the recombining hydrogen atoms that are producing the red-pink emission characteristic of the element’s spectrum. Even at a distance of over 7,000 light-years, the star-forming region is so large that it spans five times the size of the Full Moon.
Ironically, while the nebula’s shape evokes thoughts of Valentine’s Day, it is located in the constellation Cassiopeia—the mythological queen of Ethiopia whose vanity drove her to boast that her daughter Andromeda was more beautiful than the daughters of the god Poseidon. As retribution, Poseidon sent a sea monster (depicted as the constellation Cetus) to ravage the kingdom. King Cepheus, wishing to spare his country from devastation, consulted an oracle and was told he must sacrifice his daughter to the sea monster. Andromeda was chained to a mountain and awaiting her fate when the warrior Perseus—riding the winged horse Pegasus—came upon her and used the severed head of Medusa to turn the sea monster to stone and save the princess from being devoured. In gratitude, Cepheus and Cassiopeia offered Andromeda’s hand in marriage to Perseus.
As punishment for her boastfulness, Cassiopeia was placed in the heavens after her death and is found near the north celestial pole where she spends half of her diurnal motion on her head. The other characters of the legend can also be found as constellations.