Cassiopeia

cassiopeia-lowThe prominent ‘W’ or ‘M’ shaped formation of stars known as Cassiopeia graces the far northern skies and represents the mythological Queen Cassiopeia, wife of King Cepheus and mother to Andromeda, the beautiful maiden rescued by Perseus. When favourably placed, the entire constellation can be seen from locations to the north of latitude 12°S, with portions of Cassiopeia visible from Australia, South Africa and all but the southernmost reaches of South America. Cassiopeia stands out quite well and should be spotted fairly easily by observers at mid-northern latitudes.

For observers in Great Britain and northern Europe Cassiopeia is a circumpolar constellation, which means that it never sets as seen from these latitudes. A good general guide to locating Cassiopeia is to use the two end stars in the ‘bowl’ of the Plough as pointers, these being the two stars we use to locate Polaris, the Pole Star and as depicted on the chart of North Circumpolar Stars. Following the imaginary line from Merak through Dubhe and past Polaris as shown will eventually bring you to Caph in Cassiopeia from where the rest of the group can be picked out.

Cassiopeia lies within the Milky Way and the whole area in and around this group is seen to abound with stars. On a really dark, clear and moonless night you should spot around fifty naked eye stars within the group, although binoculars will reveal many more scattered across this region of sky. Although most of these stars are below naked-eye visibility, their combined light produces the effect we call the Milky Way. While not usually very clear to city-dwellers, the Milky Way can be a superb sight when viewed under a really dark and moonless sky.

Cassiopeia contains six prominent stars, the brightest of which is Cih whose light has taken around 550 years to reach us. Cih generally shines at magnitude 2.15, although this star is slightly variable and prone to sudden and unpredictable increases in brightness. Shedar, its name derived from the Arabic ‘al-sadr’, meaning ‘the Breast’, is a magnitude 2.24 orange giant star. Shining from a distance of around 220 light years, the orange tint of Shedar is easily seen in binoculars. Slightly fainter than Shedar is Caph, a white giant shining at magnitude 2.28 and lying at a distance of just 55 light years. Caph derives its name from the Arabic ‘al-kaff al-khadib’ meaning ‘the Stained Hand’, an allusion to the Eastern tradition of staining the finger-tips with henna leaves. Achird, located between Shedar and Cih, is a comparatively nearby star, its magnitude 3.46 glow reaching us from a distance of just 19.4 light years.

Marking the knee of Cassiopeia is magnitude 2.66 Ksora, the light from which set off on its journey towards us around a century ago. An alternative name for this star is Ruchbah, both names being derived from the Arabic ‘rukbat dhat al-kursiy’ meaning ‘the Knee of the Lady in the Chair’. The star Segin completes the distinctive shape of Cassiopeia. Segin shines at magnitude 3.35 from a distance of around 425 light years, the light we are seeing from this star today actually having set off towards us before the invention of the telescope in the early-1600s!

 

SEEK OUT AN OPEN STAR CLUSTER

m52-in-cassiopeia-noao-aura-nsfCassiopeia plays host to a number of open star clusters within reach of binoculars or small telescopes, one of which is Messier 52 (M52), discovered by the French astronomer Charles Messier in 1774. This collection of around 200 stars shines with an overall magnitude of 7.3 and is thought to lie at a distance in excess of 5,000 light years. M52 can be found close to the star 4 Cassiopeiae, lying more or less on a line taken from Shedar through Caph, and you can track it down by star m52-finder-chart-lowhopping through the field of stars from Caph as shown on the finder chart. During your search, remember to look for a small patch of light rather than an actual gathering of stars. Once M52 is located, binoculars will reveal it as a misty cloud, although even a small telescope will bring out a number of individual stars within this fine open star cluster.

 

This prominent constellation was alluded to by the English astronomer Joseph Henry Elgie (right) when he was recalling his original efforts to find his way around the night sky. joseph-henry-elgieAs he informs us, a number of the constellations that he struggled to identify were rather faint and difficult to detect, although he had no problems with Cassiopeia, writing that: ‘Facing due north, and looking high upward, the gaze meets with five stars of nearly equal brightness, in form resembling a sprawling capital “W”. They make the principal outline of the constellation Cassiopeia, the Lady in the Chair. I cherish a kindly remembrance for Cassiopeia; it was the first star group I ever recognised, when, under almost heart-breaking difficulties, I was trying to learn the geography of the sky’.

Why not take time out to look for the distinctive shape of Queen Cassiopeia, and perhaps bring to mind Elgie’s wonderful comments on this beautiful pattern of stars…

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