Cassiopeia, the Queen, is a northern constellation that is circumpolar for observers north of 35 degrees north latitude. Circumpolar means that it is visible above the horizon continuously as it circles around the north celestial pole during the night as the Earth turns.
Hold your mouse cursor over the image to see constellation figures, boundaries, and star identifications.
The main outline of the constellation is easy to pick out in the sky at night by its five main stars which form the shape of the letter "M" when the constellation transits the meridian above the north celestial pole at around midnight in the fall. When Cassiopeia is below the north celestial pole it is seen in the shape of the letter "W" as it has turned upside down.
Alpha Cassiopeiae is traditionally called Shedar, or Shedir, which means the "Breast" or heart of the constellation in Arabic. Many star names have an Arabic origin. It is a spectral-class K-type orange-colored giant star that shines at an apparent magnitude of 2.24. It is located 229 light-years away from the Earth. Shedar is an optical double star with a ninth-magnitude companion that is separated by 64 arcseconds.
Beta Cassiopeia is known as Caph, which means the "Palm" in Arabic. It is a spectral-class F-type white Delta Scuti type variable star that shines at an apparent magnitude of 2.25 to 2.31. It is located 54 light-years away from the Earth.
Gamma Cassiopeiae is known as Tsih or Cih, which means the "Whip" in Chinese. It is a spectral-class B-type blue variable star that shines at an apparent magnitude of 1.6 to 3.0. It is located 613 light-years away from the Earth.
Delta Cassiopeiae is known as Ruchbah, which means the "Knee" in Arabic. Ruchbah is a spectral-class A type blue-white star that is an Algol-type eclipsing variable star whose magnitude varies from 2.68 to 2.76. It is located 99 light-years from Earth.
Epsilon Cassiopeiae is known as Segin. It is a spectral-class B type blue-white star that shines at magnitude 3.3. It is located 442 light-years from Earth.
This bright section of the Milky Way is strewn with thousands of individual stars, star clouds, dark nebulae, red emission nebulae, and glittering star clusters. As we look at Cassiopeia, we are looking out into one of the outer arms of our own Milky Way Galaxy, and away from the galaxy's center in Sagittarius.
Another very large complex of red emission nebulae, Ced 214 and NGC 7822 lie near the center of the bottom of the frame. Open cluster NGC 7789 is to the left of Caph, and open clusters NGC 457, M103 and NGC 663 are near Ruchbah (Delta Cassiopeiae).
Cassiopeia was cataloged by the Greek astronomer Ptolemy in the second century C.E. (Common Era). It is the 25th largest of today's 88 modern constellations, covering 598 square degrees of sky.
North is to the lower right in the above image.