Aquarius and Capricornus

Andromeda is one of the most prominent constellations in the evening sky in autumn and early winter. It is also quite easy to find, with its three brightest stars almost in a straight line immediately east of the Great Square of Pegasus. All three of these stars are second magnitude and one of them, Alpheratz, although deemed to belong to Andromeda is actually one of the corner stars of the Great Square of Pegasus.

The middle star of the three, Mirach, leads us to Andromeda’s showpiece, the Great Andromeda Nebula, M31. This is close to the second of two fainter stars in a line north of Mirach, more or less at right angles to the line of the three bright stars. On a dark night with a clear sky it can be seen quite easily with the naked eye, being about magnitude 3.5. M31 is the nearest major galaxy to our own Milky Way and the largest galaxy in the so-called “Local Group”. It contains some 200 million stars – about twice as many as the Milky Way. This means that, despite its immense distance – over 2 million light years, M31 is such a large object that the best views of it are in fact through good binoculars rather than a telescope. Under good conditions, binoculars might also pick up the two eighth magnitude satellite galaxies M32 & M110 and these two are certainly well seen in even a small telescope.

The last of Andromeda’s three main stars, Almach, is one of the finest doubles in the sky, consisting of a golden second magnitude primary and a bluish fifth magnitude secondary. The separation (10 seconds of arc) means that they can be comfortably split even by quite small telescopes. The companion star is double again but the separation of this pair is too small for amateur instruments. The brightest member of the close pair is itself a spectroscopic binary, so that Almach is in fact a quadruple system.

Fairly close to Almach is the open cluster NGC 752, a large cluster of fairly bright stars, which like M31 is better observed in binoculars than telescopes. A different proposition altogether is the edge-on spiral galaxy NGC 891, about ten times further away than M31. Due to its low surface brightness an aperture of at least 6”, a dark sky and excellent conditions are required to be able to see it. Finally in Andromeda the “Blue Snowball” planetary nebula (NGC 7662) is worth tracking down if you have a telescope. It is an excellent example of an object which is far more conspicuous with averted vision than when viewed directly.

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