Cassiopeia - The Mythology behind the Constellation

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Cassiopeia is a conspicuous W - shaped constellation located near the north celestial pole, roughly opposite the Big Dipper in relation to the celestial pole1. The constellation covers an angular area of about 598 square degrees, ranking 9th largest of the internationally recognised constellations.

Cassiopeia is associated with the Perseus constellation family, which extends approximately parallel to the Milky Way and includes Cepheus, the royal consort of Cassiopeia lying to the north and west of the Lady; Andromeda; the body of Perseus; Pegasus; the Whale Cetus2; and the Charioteer Auriga.
In Arabian countries, Cassiopeia is called Caph (or Beta Cas).

  • Abbreviation: Cas
  • Genitive: Cassiopeiae
  • Translation: Queen of Ethiopia or Andromeda's Mother
  • Interactive Star Chart

Position in the Sky:

  • Right Ascension: 1 hour
  • Declination: 60 degrees
  • Visible between latitudes 90 and -20 degrees
  • Best seen in November (at 9:00 PM)

Stars and Other Objects


  • Irregularly variable stars
    • Alpha Cas
    • Gamma Cas
  • Double star
    • Eta Cas
  • Triple star
    • Iota Cas
  • Variable Star
    • Rho Cas
  • Diffuse Nebulae
    • I 1805
    • I1848
    • I 59
    • NGC 281
  • Planetary Nebula
    • NGC 7635
  • Open star clusters
    • M52
    • M103
    • NGC 663
    • NGC 129
    • NGC 133
    • NGC 146
    • NGC 457
    • NGC 559
    • NGC 654
    • NGC 663

In more detail...

The leading star in the constellation is Alpha Cas, or Shedir (Arabic for The Breast). This is an irregular variable star,3 which forms an optical double star, meaning that they are not physically interactive, they just appear together as seen in the sky form Earth with a 9th magnitude blue naieghbour star.

Gamma Cas, sometimes called Tsi (Chinese for The whip), is an unstable blue subgiant4, throwing off shells of gas at unpredictable intervals- its brightness therefore varies between 2nd and 3rd magnitude.

The double star Eta Cas consists of a yellow5 and a red6 component, and is impressively beautiful even when using relatively small telescopes. The two stars are of 3.44 and 8th magnitude respectively.

Iota Cas is good example of a triple star. Looking at the white 4.5 magnitude star with a small telescope reveals an 8th magnitude companion star. The brighter component has a close 7th magnitude companion, but for separation a telescope with an apature of at least 100 mm and a high magnification is needed.

Rho Cas is another variable star, which can be viewed with the naked eye and appears yellow. Its variation period is unknown.

The region is also home to a large number of nebulae and open clusters:

Next to gamma Cas is the diffuse nebula I59, which consists of two fans pointing northwest.

One degree west of alpha Cas is the diffuse nebula NGC 281.

The planetary nebula NGC 7635 makes good viewing even with small telescopes as it has an high total brightness, but appears faint due to its large extension.

Of the local open clusters the two Messier objects M52 and M103 are probably the most well known. The first is shaped roughly like a kidney and contains over 100 stars. It is a good object for small telescopes and binoculars, showing a prominent 8th magnitude star at one edge. The second Messier object has the shape of a fan and at least 40 members 7.

The cluster NGC 457 also deserves a mention as it is one of the brightest in the sky and is an interesting and attractive target for small telescopes; the stars seem to follow a chain- like structure.

Another star which makes for good viewing is phi Cas, a 5th magnitude yellow supergiant8.

The Myth of Perseus

...This is my contribution and will come later as soon as I've checked my facts.

1For the astrophiles, it is located between a declination of +50 and +60, and between a right ascension of 3h and 23h.2Also belongs to the family "Heavenly Waters".3Spectral type K0IIIa.4Spectral type B0IVe.5Spectral type G0V.6Spectral type M0.7more information about both objects can be obtained from the Messier Database8Spectral type F0Ia

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