Cassiopeia Constellation Facts

Cassiopeia is one of the brightest and most recognizable constellations in the night sky.

Cassiopeia is visible all year in the Northern hemisphere.
The constellation is visible in some northerly regions of the Southern hemisphere in late spring.
The combination of its simple 'w' shape and the brightness of its stars makes Cassiopeia one of the most easily recognizable constellations in the night sky.
If we were able to observe the sun from the nearest star system Alpha Centauri, it would appear in the constellation of Cassiopeia.
Schedar is the brightest star in the constellation, it is 40 times larger in diameter than the sun.
The supernova remnant "Cassiopeia A" lies within the boundaries of the constellation, supernova remnants are nebulas which form after the explosion of a large star.
The Pacman Nebula, named after its resemblance to the old video game character, also lies within the constellation.
Cassiopeia is one of the ancient constellations catalogued by the Greco-Roman astronomer Ptolomy almost 2,000 years ago.

Cassiopeia Mythology

Queen Cassiopeia spinning on her throne in the night sky.

Cassiopeia was a queen from Greek mythology whose legendary vanity and arrogance ultimately led to her downfall. Cassiopeia was the wife of King Cepheus of Aethiopia and mother to the beautiful Princess Andromeda. One day Cassiopeia proclaimed to the Nereids, female spirits of the sea famed for their beauty, that both she and her daughter were more beautiful and radiant than any of them.

The Nereids passed on their displeasure at Cassiopeia’s vain comments to the sea god Poseidon who immediately dispatched a sea monster to destroy Aethiopia. Shocked at the attack Cepheus consulted an oracle who advised him that the only way to appease Poseidon was to sacrifice their daughter. Cepheus and Cassiopeia accepted the advice and chained their daughter to a rock as an offering to the sea monster, luckily for Andromeda she was rescued by the hero Perseus. As an alternative punishment Poseidon sent Cassiopeia into the heavens, spinning around on her throne for eternity.

Main Stars in the Cassiopeia Constellation

The number next to each star is its apparent magnitude, its brightness from our point of view on Earth, the lower the number the brighter the star in the night sky.

Segin
Also known as Epsilon Cassiopeiae, Segin is a blue giant star around 400 light years from Earth, it has a mass around 9 times that of the sun and a diameter around 6 times greater. The star has surface temperatures around 3 times greater than the sun and is around 2,500 times more luminous.

Ruchbah
Also known as Delta Cassiopeiae, Ruchbah appears as a single star in the night sky but is actually a pair of binary stars, the larger of the two stars is a white subgiant around 4 times larger in diameter than the sun.

Gamma Cassiopeiae
With no traditional name this star is known as Gamma Cassiopeiae, located around 550 light years from Earth Gamma Cassiopeiae is a blue subgiant with a mass almost 20 times greater than the sun and a diameter around 15 times greater. It is over 50,000 times more luminous than the sun with surface temperatures around 6 times hotter.

Schedar
Also known as Alpha Cassiopeiae, Schedar is an orange giant around 230 light years from Earth and is the brightest star in the constellation, it has a mass around 4 times that of the sun and a radius around 40 times larger.

Caph
Also known as Beta Cassiopeiae, Caph is a white-yellow giant star around 55 light years from Earth, it has around twice the mass of the sun with a radius around three and a half times larger.

Note: It may look like east and west are the wrong way wrong round on star charts but they are designed to be used as if they are being held above the head.

Finding Cassiopeia - Northern Hemisphere

The chart shows the position of Cassiopeia over most of the United States in mid-autumn at 10 pm. This chart can also be applied to other areas of the Northern hemisphere such as Canada, the UK and Europe. In the Northern hemisphere Cassiopeia never sets below the horizon, as a result it is visible all year in the night sky.

From January to March the constellation will first appear almost overhead around 6 pm, as the evening progresses it will head down towards the horizon in a north-westerly direction, by early morning Cassiopeia will be low on the horizon in a more northerly or north-easterly direction.

From April to June Cassiopeia will be visible low on the horizon in a northerly or north-westerly direction at around 9 pm, moving eastwards it will stay quite low in the sky for several hours before beginning to rise higher around 2 am.

From July to September the constellation will be visible from around 10 pm in a northerly or north-easterly position, as the night progresses it will end up almost directly overhead before day breaks.

From October to December it will appear high in the sky in the north-east at around 6 pm, within a few hours the constellation will move overhead before dipping back down towards the horizon in a north-westerly direction.

Finding Cassiopeia - Southern Hemisphere

The chart shows the position of Cassiopeia over Northern Australia in late-spring at 9 pm. This chart can also be applied to more northerly areas of the Southern hemisphere. In Southern Australia and other southerly regions of the hemisphere Cassiopeia is not visible.

The best time to view Cassiopeia is in November and December although the constellation will be low on the horizon, it will first appear around 10 pm in a northerly direction and be visible for a few hours as it heads westwards before dipping below the horizon between 1 and 3 am.