The Cassiopeia Constellation

The Cassiopeia Constellation.

Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive ‘W’ shape, formed by five bright stars. It is opposite the Big Dipper. In northern locations above latitude 34ºN it is visible year-round, and in the (sub)tropics it can be seen at its clearest from September to early November. Covering 598.4 square degrees and hence 1.451% of the sky, Cassiopeia ranks 25th of the 88 constellations in the area. It is bordered by Cepheus to the north and west, Andromeda to the south and west, Perseus to the southeast and Camelopardalis to the east, and also shares a short border with Lacerta to the west. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 00h 27m 03s and 23h 41m 06s, while the declination coordinates are between 77.69° and 46.68°. Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 12°S. High in the northern sky, it is circumpolar (that is, it never sets in the night sky) to viewers in the British Isles, Canada and the northern United States.

The five brightest stars of Cassiopeia – Alpha, Beta, Gamma, Delta, and Epsilon Cassiopeiae – form the characteristic W-shaped asterism. Alpha Cassiopeiae, traditionally called Schedar (from the Arabic Al Sadr, “the breast”), is a multiple star. The primary is an orange-hued giant of magnitude 2.2, 228 light-years from Earth. With a luminosity of around 771 times that of the Sun, it has swollen and cooled after exhausting its core hydrogen over its 100 to 200 million-year lifespan, spending much of it as a blue-white B-type main-sequence star. The brightest companion is a magnitude 8.9 yellow dwarf widely separated from the primary, while two other companions are closer and magnitudes 13 and 14 respectively. Beta Cassiopeiae, or Caph (meaning “hand”), is a white-hued star of magnitude 2.3, 54.7 light-years from Earth. Around 1.2 billion years old, it has used up its core hydrogen and begun expanding and cooling off the main sequence. It is around 1.9 times as massive as the Sun, and around 21.3 times as luminous. It is a Delta Scuti variable. Gamma Cassiopeiae is the prototype Gamma Cassiopeiae variable star, a type of variable star that has a variable disc of material flung off by the high rotation rate of the star. It has a minimum magnitude of 3.0. It is a spectroscopic binary, with an orbital period of 203.59 days and a companion with a calculated mass about the same as the Sun. However, no direct evidence of this companion has been found, leading to speculation that it might be a white dwarf or another degenerate star. Delta Cassiopeiae, also known as Ruchbah or Rukbat, meaning “knee,” is an Algol-type eclipsing binary star. Epsilon Cassiopeiae has an apparent magnitude of 3.3. Located 410 ± 20 light-years from Earth, it is a hot blue-white star of spectral type B3 III with a surface temperature of 15,680 K. It is 6.5 times as massive and 4.2 times as wide as the Sun, and belongs to a class of stars known as Be stars—rapidly spinning stars that throw off a ring or shell of matter.

A rich section of the Milky Way runs through Cassiopeia, stretching from Perseus towards Cygnus, and it contains some open clusters, young, luminous galactic disc stars, and nebulae. The Heart Nebula and the Soul Nebula are two neighbouring emission nebulae about 7,500 light-years away. Two Messier objects, M52 (NGC 7654) and M103 (NGC 581) are located in Cassiopeia; both are open clusters. M52, once described as a “kidney-shaped” cluster, contains approximately 100 stars and is 5200 light-years from Earth. M103 is far poorer than M52, with only about 25 stars included. The other prominent open clusters in Cassiopeia are NGC 457 and NGC 663, both of which have about 80 stars. There are two supernova remnants in Cassiopeia. The first, which is unnamed, is the aftermath of the supernova called Tycho’s Star. It was observed in 1572 by Tycho Brahe and now exists as a bright object in the radio spectrum. Two members of the Local Group of galaxies are in Cassiopeia. NGC 185 is a magnitude 9.2 elliptical galaxy of type E0, 2 million light-years away. Slightly dimmer and more distant NGC 147 is a magnitude 9.3 elliptical galaxy, like NGC 185 it is an elliptical of type E0

The December Phi Cassiopeiids is a recently discovered early December meteor shower that radiates from Cassiopeia. Phi Cassiopeiids are very slow, with an entry velocity of approximately 16.7 kilometres per second. Credit: Wikipedia.