Cassiopeia (constellation) (original) (raw)

Cassiopeia is a northern constellation representing the legendary queen of Ethiopia Cassiopeia, who was the wife of Cepheus and the mother of Andromeda. It is one of the 88 modern constellations, and was also one of the 48 listed by Ptolemy.

Notable features

Five of the stars of Cassiopeia form a W shape, which is one of the most distinctive patterns in the northern sky. Since it is close to the north celestial pole, it remains in the sky all night long in most northern countries.

It is frequently used as a rough indicator of sidereal time; the leading bright star of the W, β Cassiopeiae, called Caph, lies almost at zero hours right ascension and hence a line drawn through Polaris and β Cassiopeiae must pass close to the vernal equinox. The hour angle of this line must be equal to sidereal time. Hence, when β Cassiopeiae is on the meridian directly above the pole the sidereal time is zero, when on the meridian directly below the pole the sidereal time is 12 hours, etc.

γ Cassiopeiae is a peculiar variable star. The brightness varies from 1.6 to 3 magnitudes. γ Cassiopeiae is assumed to be a binary star containing a Be star and a neutron star. It is the brightest X-ray binary on the sky, no other X-ray binaries can be seen with naked eye.

Cassiopeia was the site of Tycho Brahe's supernova of 1572, and is also the location of Cassiopeia A, the strongest radio source in the sky (other than the sun). Cassiopeia A is the remnant of a supernova which apparently occurred in about 1667, although there is no record of it having been observed.

If we were to observe Earth's Sun from Alpha Centauri, it would appear to be in Cassiopeia.