Cassiopeia

Abbreviation:

Cas

English name:

Cassiopeia

Coordinates

see Stellar data

Particulars:

• Irregularly variable stars alpha Cas, gamma Cas
• Double star eta Cas
• Triple star iota Cas
• Variable star rho Cas
• Diffuse Nebulae I 1805, I 1848, 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

General:

This beautiful constellation at the edge of the Milky Way has definetely the shape of a "W". It is assiociated with the Perseus constellation family.
Sweeping this region with binoculars (or even an opera glas) is rewarding (especially the region around delta Cas).
It is located between DECL=+50 and DECL=+60, RA=23h and RA=3h. Once you found Cassiopeia or the Big Dipper, which is located opposite of the celestial pole, you can easily locate other constellations of the northern hemisphere.
In arabian countries this constellation is called Caph, which is also the name of beta Cas.

Stars and other objects

The leading star, alpha Cas, also called Shedir (arab.: the breast), is an irregular variable star (K0IIIa), which forms with an 9th mag blue neighbour an optical double star (i.e. not physically related).
Gamma Cas, sometimes called Tsi (chin.: the whip), is an unstable blue subgiant (spectraltype B0IVe), that throws off shells of gas at unpredictable intervals. So it brightness vary between 2nd mag and 3rd mag.
The double eta Cas consists of a yellow (G0V) and a red component (M0) and is really beautiful in small telescopes. The two stars are of 3.44 mag and 8th mag, respectively.
A nice triple star is iota Cas. In small telescopes a 8th mag companion to the white star of 4.5 mag is revealed. The brighter component has a close 7th mag companion, but for separation a telescope with an apertur of at least 100 mm and as high magnification is needed.
Another variable star is rho Cas. This yellow star can be viewed with the naked eye. Its variation period is unknown. (?)
In this region one can find lots of nebulae and open clusters:
The diffuse nebula I 59, lying next to gamma Cas consists of two fans pointing northwest.
One degree west of alpha Cas you find the diffuse nebula NGC 281.
The planetary nebula NGC 7635shows up an high total brightness; yet it appears faint due to its large extension. A nice object even for small telescopes.
Of the hole bunch of open clusters the two Messier objects M52 and M103 may be best known. The first is somewhat kidney-shaped and contains over 100 stars. Its a good object for binoculars showing a prominent 8th mag star at one edge. The second Messier object has the shape of a fan and at least 40 members (for more information about both objects please refer to the Messier Database).
From the other clusters NGC 457 should be mentioned for it is one of the brightest in the sky and an attractive object for small telescopes; its stars seemed to be arranged in chains. Also good viewable it the 5th mag yellow supergiant phi Cas (spectraltype F0Ia).

Mythological Background:

Long ago in ethiopia Cassiopeia has been the wife of Cepheus and the mother of Andromeda. Because she thought herself more beautiful than the daughters of Nereus, a god of the sea, she challanged the anger of the god Poseidon. To punish her, her daughter was chained to a rock of the coast as a sacrifice for a sea monster. Andromeda was saved from death by Perseus. (Publius Ovidius Naso: Metamophoses, IV)
To learn humility Cassiopeia was banned to the sky hanging half of the time head downward.