Texas Astronomical Society

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Constellations of the Month

by Rick Raasch

The constellations of Cassiopeia and Cepheus are circumpolar constellations which lie on or near to the Milky Way. As such, many open clusters are in this region, including some of the finest in the whole sky. There are also large regions of nebulosity in this area. Some of these nebulous regions are accessible with amateur instruments, but most of them are best seen in long exposure photographs. Planetary nebulae and even some galaxies are even found in this interesting and rich region.

CASSIOPEIA

M-52 This beautiful open cluster is about 12' in diameter, and is composed of relatively bright stars. The cluster is relatively concentrated to the center, and is dominated by a bright red star, and is well detached from the stellar background. It lies less than a degree away from NGC 7635, the Bubble Nebula, which is a target for larger instruments.

M-103 This is a relatively small open cluster, about 8' in diameter. I contains about 20 relatively bright stars, and is loosely gathered. It is seen through the finder scope or binoculars as a slightly hazy patch.

NGC 457 The "Owl" Cluster. This fine cluster is composed of 75-100 bright stars which form the shape of an owl with spread wings and the bright double star Phi Cas as its eyes. This cluster and its distinctive shape are easily seen in binoculars.

NGC 663 Lying very close to M-103, this fine open cluster is more impressive than that object. It is somewhat resolved in binoculars, and is well detached from the background. It consists of 10-12 bright stars and about 50 fainter stars, and is moderately concentrated to the center.

NGC 7789 One of my favorite objects, this cluster is about 15' in diameter and composed of hundreds of stars. The stars are about 10-11 magnitude, but their numbers and compact size makes this open cluster resemble a loosely gathered globular cluster. I consider this a real showpiece object.

Eta Cas This is a very pretty and easily split double star which shows a yellow-white primary and a red-gold secondary. Check it out.

CEPHEUS

NGC 40 This is a fine planetary nebula. It is relatively large, about 50" in diameter, and is seen as a grey halo surrounding a bright central star. The eastern and western sides of the nebula appear to be brighter than the rest.

NGC 6939 This is a rather nondescript open cluster which is only remarkable in that it lies in the same low power field of view with a galaxy, NGC 6946 in Cygnus, and together they are striking. 6939 is moderately well detached, and is composed of many faint stars in a 6'x4' area. 6946 is 5-6' in diameter, roughly circular, and relatively faint. Averted vision hints at dark lanes, indicating its identity as a face on spiral galaxy.

NGC 7160 This open cluster is about 6'x2', extended east-west, and is composed of about 20 moderately bright stars. It is well detached from the background, at the brighter stars are aligned along its axis, forming 2 groups of triangles.

Next Month: Andromeda and Perseus