Visible at latitudes between +90° and −20° Best visible at 21:00 (9 p.m.) during the month of November
Cassiopeia is a northern constellation which Greek mythology considered to represent a vain queen. It is one of the 88 modern constellations, and was also one of the 48 listed by Ptolemy.
Cassiopeia contains two stars visible to the naked eye that rank among the most luminous in the galaxy: ρ Cas and V509 Cas.
If we were to observe Earth's Sun from Alpha Centauri, it would appear to be in Cassiopeia, at about 0.5 magnitude. Roughly speaking, the \/\/ of Cassiopeia would become a /\/\/, with the Sun at the leftmost end, closest to ε Cas.
γ Cas is a peculiar variable star. The brightness varies from 1.6 to 3 magnitudes. γ Cas is assumed to be a binary star containing a Be star and a neutron star. It is the brightest X-ray binary on the sky, no other X-ray binaries can be seen with the naked eye.
Cassiopeia A: Cassiopeia was the site of Tycho Brahe's supernova of 1572 (SN 1572), and is also the location of Cassiopeia A, the strongest radio source in the sky (other than the sun). Cassiopeia A is the remnant of a supernova which apparently occurred in about 1667, although there is no record of it having been observed.
Using images captured by the Spitzer Space Telescope, an analysis of dust cloud movement around the supernova showed some of the clumps and filaments were in the wrong position to have been energized by the original explosion. Estimates indicate that a more recent outburst from the neutron star occurred in 1953. After calculating the direction of the outburst, it was found that this event could not have been seen from Earth. Krause speculates that the object may be a magnetar. (Krause, et al., 2005)
ρ Cas is a yellow hypergiant, one of the largest known stars. Its size is approximately 738 times larger than our Sun.
Notable deep sky objects
M103: Discovered by Pierre Méchain in 1781, this open cluster with an apparent brightness of 7.4m lies at a distance of approximately 8,130 ly. The cluster occupies a field 6' in diameter. M 103 can be seen with 7x35 binoculars about 1 degree northeast of Delta Cassiopeiae, but is best viewed using a telescope at low magnifications. W5 is a large star-forming region in Cassiopeia lying about 7,000 light years away.
Mythology
Viewing the fainter stars, visible to the naked eye, renders the constellation a human figure, sitting on a chair. As it is near Polaris, in the northern hemisphere it can be seen the whole year, although sometimes upside down whilst in the chair [link]. The Greeks considered that this was an undignified position (being upside down, and also the normal way up, in a chair), and must be a suitable punishment for some crime. Since the punishment was one of losing dignity, vanity is a suitable crime. There may have been some influence from the Greek form of her name: Κασσι-επεια = "she whose words excel".
Together with other constellations nearby (Andromeda, Perseus, Cepheus, and possibly Pegasus), and the constellation Cetus below Cepheus, and Pisces, this may be the source of the myth of the Boast of Cassiopeia, with which it is usually identified.
Scott: "This is wrong. This is north. The map is flipped."
Jones: "How do you know it's north?"
Scott: "See that? That's Cassiopeia. That's my girlfriend."
