Cassiopeia is one of the most recognizable constellations in the night sky, and being circumpolar can be seen all year round from northern latitudes, as well as from some regions in the Southern hemisphere (-20°) in late spring. This beautiful constellation is most noted for its asterism of five stars which form a giant “M” or “W” as it rotates around the north star Polaris throughout a 24 hour period. Of course, we can only see its night-time rotation as the Sun blocks our view during the daytime. Throughout the year Cassiopeia often appears as a “W” in the Spring and Summer, and as a “M” in Autumn and Winter.
Cassiopeia is named after a vain Ethiopian queen from Greek mythology, and is surrounded in the night sky by a family of constellations associated with the legend of Perseus, including the hero’s winged horse Pegasus, the queen’s husband Cepheus, her daughter Andromeda, and the sea monster Cetus.
Cassiopeia, mother of Andromeda, was a woman who prized vanity above respect for the Gods, which in ancient Greece was not the wisest of decisions for our self-absorbed heroine. She even boasted that her beauty, and that of her daughter Andromeda, was greater than that of the Nereids (sea nymphs) and so, naturally, the fabled sea-god Poseidon himself took offense and sent a sea monster (Cetus) to ravage their kingdom. Perseus on his winged-horse Pegasus subsequently rescued Andromeda from Cetus, whom her father (Cepheus) and mother (Cassiopeia) had tied to a rock to appease the monster, and so Poseidon decided to punish Cassiopeia all the same by tying her to a chair and placing her in the heavens where she still circles the northern sky, spending half her time upside-down.
We usually associate Cassiopeia with its five main luminous stars which make up the majority of the constellation, although there are actually 53 Bayer/Flamsteed designated stars:
– Gamma Cassiopeia, the constellation’s brightest star, is a blue (B0.5 IVe) variable star located nearly 600 light years away whose visual magnitude ranges between 1.6 and 3.0. It has a mass 15 times greater than our sun, shines 40,000 times brighter, and forms the central most star in the traditional ‘W’ shape of the constellation.
– Schedar (Alpha Cassiopeia), the second brightest star in Cassiopeia, is an orange giant (K0IIIa) found about 280 light years from our solar system that shine with a magnitude of 2.24. Its name means ‘breasts’ in Arabic, as it marks the location of the queen’s heart.
– Caph (Beta Cassiopeia), the constellation’s third brightest star, is a yellow-white giant (F2 III-IV) situated around 50 light years from Earth that has an apparent magnitude of 2.27. It is almost 4 times the size of the Sun, and is around 30 times brighter. The word Caph is Arabic, and refers to the ‘palm’ of a hand.
Other stars of interest in Cassiopeia includes Ruchbah (Delta Cassiopeia), a binary star system 100 light years distant, whose name means the ‘knee’; Segin (Epsilon Cassiopeia), a blue-white giant 440 light years away that is 2,500 times brighter than the Sun; as well as the yellow-white stars Achird (Eta Cassiopeiae) and V509 Cassiopeiae; the yellow hypergiant Rho Cassiopeiae; and the blue-white subgiant Zeta Cassiopeiae.
Notable Deep Sky Objects
Cassiopeia lies in a phenomenal Milky Way star field, meaning that there are a number of impressive deep-sky objects (DSOs) that are there for your viewing pleasure. This includes two Messier objects, namely M52 and M103, both open star cluster with the former containing around 190 stars, and the latter about 172. Two super-nova remnants can also be seen in this field, including Tycho’s Star which went supernova in 1572, and Cassiopeia A, which exploded around 1660 and is recognized as the brightest radio source in the sky, excluding the solar system.
Other notable deep sky objects in Cassiopeia includes the Pacman Nebula; the White Rose Cluster, and the dwarf spheroidal galaxies NGC 185 (Caldwell 18) and NGC 147 (Caldwell 17).
The constellation has a number of meteor showers associated with it, including the Beta Cassiopeids which is active from July 3rd to August 19th, and peaks on the July 29th with around 52 meteors per hour; and the December Phi Cassiopeiids which runs from November 26th to December 5th, but produces only one meteor per hour.
So, let’s take a moment to raise our glass to one of the most self-centered individual to ever grace Greek mythology, and give toast to the Queen of Vanity for making this beautiful constellation possible.