Brian Jones: Queen Cassiopeia
Along with the Plough (actually part of the larger constellation Ursa Major, the Great Bear) and Ursa Minor (the Little Bear), the prominent ‘W’ formation of stars known as Cassiopeia completes the trio of conspicuous star groups that grace the northern skies. Cassiopeia stands out quite well and can be spotted fairly easily, located low in the north-western sky during spring evenings. However, it can also be found by using the two end stars in the ‘bowl’ of the Plough (located high in the sky a little to the east of the overhead point) as your guide. If you follow the imaginary line from Merak, through Dubhe and past Polaris as shown below, you will eventually arrive at Cassiopeia.
The constellation represents the mythological Queen Cassiopeia, wife of King Cepheus and mother to Andromeda, the beautiful maiden rescued by Perseus from the terrible sea monster. Cassiopeia is what we call a circumpolar constellation, which means that it never sets as seen from the latitudes of Great Britain, from where it is located almost overhead in autumn. The group moves around the heavens, tracing a circle around the Pole Star, eventually skimming the northern horizon, where she can be seen over the rooftops during spring evenings.
The constellation lies within the Milky Way and the whole area is seen to abound with stars. On a really clear night you should spot around fifty stars within the group, although binoculars will reveal many fainter stars scattered across this area of sky. Although most of these stars are below naked-eye visibility, their combined light produces the effect we call the Milky Way. During spring evenings the Milky Way can be seen as a faint shining band of light spanning the sky from the north, crossing Cassiopeia and down to the south. Not usually very clear to city-dwellers, it can be a superb sight when viewed under a really dark and moonless sky.
Cassiopeia contains six prominent stars, the brightest of which is Schedir, from the Arabic Al Sadr – ‘the Breast’. Schedir is a giant star, lying so far away that its light takes over 160 years to reach us. By comparison, Caph is a dwarf, although it appears almost as bright as Schedir because it lies at a distance of only 47 light years. Another giant is Cih, a star so distant that its light set off towards us during the reign of Edward the Second. Ksora, named from the Arabic for Knee, is a white star, like most of the main stars in Cassiopeia. The exception is Schedir which has an orange tint that is detectable with the naked eye but which can be spotted more easily through binoculars.
It must be pointed out that, unless you are a fairly experienced observer, individual colours of stars do not readily stand out. The reason for this is that most of the stars we see in the night sky are not bright enough for their colours to register on our eyes, although even a modest pair of binoculars can be a great help when seeking out different star colours.
Whether you want to scan the rich backdrop of the star fields of the Milky Way or simply pick out the heavenly ‘W’, Cassiopeia is the constellation to look for. Go out there and join her under the starlit spring sky. Happy stargazing!