The Cassiopeia constellation is normally visible in the Northern sky and easily identified by its 'W' shape. Part of the Perseus family, it is visible almost throughout the year, to people in the northern hemisphere. However, it is most clearly observed in the November sky. It identifies a region in the sky that is very rich in stars. The region is abundant with emission nebulae, many star clusters, and even a supernova remnant. The image accompanying this article is that of 'Bubble Nebula', which lies in this constellation.
This constellation was identified long ago, in 2nd century AD, by the Greek astronomer Claudius Ptolemy. Knowing the constellation, makes it easy to identify many surrounding ones. It is surrounded by the Andromeda constellation on the south, Cepheus in the North, Perseus on the south east, and is opposite to the Big Dipper. It is also bordered by Camelopardalis and Lacerta constellations.
It is visible between Earth latitudes of +90° and -20°. Best viewing time in North America is around 9 pm, in the month of November. An interesting fact about Cassiopeia is that, if it is observed from Alpha Centauri (Second closest binary star system to the Sun), then our Sun would appear to be a part of it and the W shape would be seen as a zigzag pattern.
The constellation was named after a vain Queen, whose story is part of ancient Greek mythology. Cassiopeia was a queen whose boastfulness about her and her daughter's beauty and narcissism invited the wrath of the Greek Sea God Poseidon. She was supposedly set in the stars as punishment by the Gods. Most of the characters in Cassiopeia's story, including her daughter Andromeda, have their names given to constellations. The constellation is denoted in old star charts, by a queen sitting on the throne.
The coordinates of this constellation are R.A. 1 h / Dec. +60° and it falls in the NQ1 quadrant. It covers a total of 598 square degrees of the nighttime sky. Here are some interesting facts.
There are five prominent stars, that make the constellation. The brightest star is an orange giant, Alpha Cassiopeiae (α Cas), with a brightness magnitude of 2.25 and is also known as Shedar, Shadar, or Shedir. The nearest star is Achird (η Cas), which is a binary system located at a distance of about 19.42 light years away, from our Sun. Two of the most luminous stars in the entire galaxy lie in this region. One is Rho Cassiopeiae (ρ Cas), which is a yellow hypergiant star, located about 11,650 light years away from Earth. The other one is V509 Cassiopeiae (V509 Cas), located at a position which is 7800 light years away from the Sun.
Supernova Remnants and Deep Space Objects
This region is home to a prominent supernova remnant, that is one of the brightest astronomical radio sources. It is known as Cassiopeia A (R.A. 23h 23m 26s / Dec +58° 48′) and the supernova explosion that created it, must have been the last such explosion in the Milky way, that could have been seen by people on Earth, about 300 years ago. Another supernova remnant, visible in the constellation, is SN 1572 (a.k.a. Tycho's Supernova), that exploded in November, 1572.
An interesting deep space object, visible in the constellation, is an irregular galaxy, cataloged as IC 10. It was first discovered by the American astronomer Lewis Swift in 1887. Two prominent open clusters, visible in this constellation, are M52 and M103. Both are old and distant star clusters, situated far away from Earth.