Cassiopeia lies high in the northern sky in December. Like Cepheus, our target constellation last month, Cassiopeia is a circumpolar constellation. It never drops below the horizon at latitudes north of about 34°N. However, it lies highest in the evening sky in late autumn and early winter. Cassiopeia consists of five stars in the shape of a W (or an M or 3, depending on the constellation’s orientation in the sky), making it quite easy to find. Although it contains several faint nebulas, Cassiopeia’s most impressive telescopic targets are its multiple stars and star clusters.
Iota Cassiopeiae is a triple star in the eastern part of Cassiopeia. To find Iota Cas, imagine a line connecting Ruchbah to Epsilon Cas (the two stars that make the left side of the W). Extend the line past Epsilon Cas the same distance again to come to Iota Cas. Splitting this triple requires fairly high magnification and a stable atmosphere. The A and B component stars are less than 3” (arcseconds) apart, while the C star lies about 7” away.
NGC 457, the Owl Cluster, is one of the most intriguing open star clusters in Cassiopeia. True to its name, this cluster does slightly resemble an owl. Two brighter stars mark the owl’s eyes, while two intersecting bars of stars make up its body and outstretched wings. Once again, the stars on the left side of Cassiopeia’s W point to our target. This time, start at Epsilon Cas, and imagine a line extending through Ruchbah. Continue the line about half that distance again to reach the Owl Cluster. One of the stars marking an eye of the owl is bright enough to be faintly visible to the unaided eye, making the cluster quite easy to locate. Binoculars will show a tiny knot of stars around this brightest one, but a telescope is necessary to really see the cluster well.
A couple other open clusters also lie near Ruchbah. M103 lies 1° northeast of the star, and NGC 663 lies about 1.5° northeast of M103. While neither of these clusters is really a showstopper, they are easily worth looking at while you’re in the area. Binoculars show both clusters as fuzzy spots, while a telescope at low to moderate magnification is needed to really observe them well.
Achird, or Eta Cassiopeiae, is one of Cassiopeia’s most beautiful double stars. Achird is the brightest star that lies just east of the line connecting Navi and Shedir, the stars at the middle and bottom left points of the W. Achird’s primary component star is light yellow, while the companion star is a rich orange. The two stars are separated by about 13”, so low magnification gives a nice tight split.
Two more rich open clusters lie on the west side of Cassiopeia—M52 and NGC 7789. To find M52, draw an imaginary line connecting Shedir to Caph (the two stars on the right side of the W). Continue the line the same distance again past Caph; then go about a degree farther to get to M52. This concentrated cluster stands out nicely from the background stars, and it shows up well in a telescope at moderate magnification.
If M52 is a good cluster, then NGC 7789 is great. To find this cluster, make a line once again from Shedir to Caph. This time, turn 90° to the right (southwest) and go about 3° to get to the cluster. NGC 7789 contains several hundred stars, with a couple of nearly starless lanes winding through it. Low to moderate magnification will give the best views of this cluster. Without question, NGC 7789 is one of the gems of the December sky.
