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Cassiopeia - The Queen

Cassiopeia is a fall constellation and occupies an area between the north celestial pole and the constellation Andromeda. It is a "W"-shaped figure, surrounded by Andromeda (Cassiopeia's daughter) and Cepheus (Cassiopeia's husband). Cassiopeia is opposite the pole from Ursa Major, the Great Bear, and it lies along the rich northern Milky Way. For observers in the Northern Hemisphere, it can be seen throughout the year. However, Cassiopeia is highest in the sky during the late summer and fall. Cassiopeia belongs to the Perseus family of constellations, along with Andromeda, Auriga, Cepheus, Cetus, Lacerta, Pegasus, Perseus, and Triangulum.

History and Mythology

Cassiopeia was the wife of the ancient King Cepheus of Ethiopia. Cassiopeia is said to have insulted the Nereids (sea nymphs) by boasting that she was more beautiful than they. The Nereids appealed to Poseidon who then sent a giant whale (Cetus) to ravage the coast of King Cepheus' kingdom. Cassiopeia and Cepheus sought the help of the oracles, who told them to sacrifice their only daughter, Andromeda, to the whale. With great despair, they had Andromeda chained to the rock for the whale to find. However, at the last minute, Andromeda was saved by Perseus, the hero, on his way home from slaying Medusa.

The very bright "star" is actually Tycho's supernova, which occurred in 1572.
During Perseus' and Andromeda's wedding, Phineus (Cepheus' brother) claimed that Andromeda was promised to him first. Perseus objected to this claim and a fight broke out. Being outnumbered, Perseus had to resort to using the head of Medusa to slay his opponents. However, Cassiopeia and Cepheus were also caught in Medusa's gaze and were turned to stone as well. Poseidon is said to have placed both Cassiopeia and Cepheus amongst the stars.

For part of the year Cassiopeia is high in the sky on her throne. But during the spring months, she appears upside down along the northern horizon. It was believed that this was her punishment for her vanity and bragging. The entire group Cassiopeia, Cepheus, Andromeda, Perseus, and Pegasus rides high in the autumn sky.

Notable Stars

Cassiopeia includes several prominent stars. The brightest is Shedar (Arabic for the "beast"), which is a variable red giant at a distance of about 230 light-years. Shedar shines with a pale pink tint.

Caph, Arabic for "hand", is Cassiopeia's second-brightest star, and represents her hand in the sky. Caph is a magnitude 2.3 blue giant. Delta Cassiopeiae, or Ruchbah, has a name derived from the Arabic word for "knee", and is a white giant star 99 light-years away.

Gamma Cassiopeiae is the middle star in the "W". American astronaut Virgil Ivan "Gus" Grissom nicknamed the star Navi, his own middle name spelled backwards. The name endured as a memorial to the astronaut, who perished in the 1967 Apollo 1 fire. Navi is a giant blue-white variable star that changes in magnitude from 3.0 to 1.6. This variation is likely caused by the varying diameter of a gaseous shell spinning around the star's equator. Gamma Cassiopeiae is 610 light-years away, and is the prototype of its class of hot, blue, rapidly-spinning variable stars.

Much closer to us is the nice double star system Eta Cassiopeiae, also called Achird, about 20 light-years away. It consists of a red dwarf and a sunlike star, magnitudes 3.5 and 7.5, orbiting each other with a period of about 500 years. Their visual separation varies from 5 to 16 arcseconds over this period.

Clusters, Nebulae, and Galaxies

M 52 is an open cluster near the far western edge of the constellation. It contains more than 100 stars of seventh magnitude and fainter. M 103 (NGC 581) is a smaller and fainter open cluster, containing somewhat fewer stars than M 52.

The Bubble Nebula, NGC 7635 (left) and open cluster M 52 (right).
The Bubble Nebula (NGC 7635) is a peculiar twelfth magnitude planetary nebula. NGC 281 is a large, triangle-shaped cloud which can be seen in an 8-inch telescope. The tenth magnitude elliptical galaxy NGC 185 is the brightest in Cassiopeia, and it is located along the southern border. It is an outlying satellite of the Andromeda Galaxy, M 31.

NGC 7789, nicknamed Caroline's Rose after its discoverer Caroline Herschel, is another large, splendid seventh magnitude open cluster which Charles Messier missed. At least 150 stars are visible in this cluster, which is estimated to be 8000 light-years distant. Other open clusters in Cassiopeia worth viewing include NGC 457, the seventh magnitude Owl Cluster; NGC 559, a small spray of ninth magnitude stars; and NGC 663, a group of 70 young class B stars.

The so-called "Heart" and "Soul" nebulae, IC 1805 and IC 1848, form a large complex of stars associated with faint nebulosity. Due to their large size, they are best seen in binoculars or rich-field telescopes. The distances to the Heart and Soul nebulae are well determined, mainly because they have star clusters at their centers. These nebulae are located in the Perseus Arm of the Galaxy, 7500 and 6500 light-years away, respectively.

For larger telescopes, IC 59 and IC 63 two arc-shaped nebulae associated with the extremely luminous star Gamma Cassiopeiae. They are a combination of emission and reflection nebulae. NGC 281 is an emission nebula, nicknamed the "Pacman Nebula" for its resemblance to the video game character. It is visible in amateur telescopes from dark sky locations.

NGC 187 and NGC 185 are both ninth magnitude dwarf elliptical galaxies. Both are outlying satellites of the great spiral galaxy M 31 in Andromeda.

In 1572, a new "star" appeared in Cassiopeia. It was observed by the Danish astronomer Tycho Brahe. For some weeks it appeared brighter than Venus in the sky, and could be seen in the daytime. This supernova is known today as "Tycho's Supernova", and it took place at an estimated distance of about 11,400 light-years.