Beginner's guide

Learning your way around the sky

Look up into a dark, clear sky, and it will seem crowded with stars. Yet appearances tend to be deceptive. If you can see as many as 2000 stars at any one time, you are doing very well indeed.

The stars form patterns called constellations. Because the stars are at different distances from us, we are dealing with nothing more than line of sight effects and the constellations mean nothing at all; two stars side by side may be widely separated, with one actually being far in the background. The constellations have been given names, which again have no significance.

The names we use are taken from the names originally given to the patterns by the ancient Greeks. But if we had followed, say, the Chinese system, our maps would look completely different, but the stars themselves would be exactly the same. The names are romantic - some mythological, some given to living things and others inanimate objects. We usually use the Latin names, since Latin is still the universal language of science.

Stars are graded into magnitudes according to their apparent brightness. The stars are graded similarly to a golfer's handicap, with the more brilliant stars having the lowest values, 1 brighter than 2, brighter than 3 and so on. On a clear night most people can see down to magnitude 6.

The stars are so remote that they do not move relative to each other, so to all intents and purposes the constellation patterns are permanent. The trick is to start by learning one or two which cannot be missed, and use these as pointers.

For example, take Ursa Major, the Great Bear, which never sets over Britain. Its seven main stars (magnitude 2 to 3) make up the characteristic pattern often called the Plough. The two end stars, Merak and Dubhe, point to Polaris in Ursa Minor (the Little Bear), which marks the north pole of the sky, and hardly seems to move at all. Follow round the Great Bear's 'tail'. And you will come to the brilliant star Arcturus, in Bootes (the Herdsman), of magnitude 0.

Another splendid guide is Orion, the Hunter, which dominates the night sky in winter (in summer it is too close to the sun to be seen). It has two first magnitude stars, the orange-red Betelgeux and the pure white Rigel. There are three 2nd magnitude stars forming the Hunter's 'belt'. Downward these point to Sirius in Canis Major, the Great Dog, which is the brightest star in the sky at a magnitude of minus 1.5. Upward, to the orange-red Aldebaran in Taurus, the Bull, of the 1st magnitude. Using this method you can soon find your way around - the stars become so much more interesting when you know which is which.

Incidentally, only the brightest stars have been given names; the rest have catalogue numbers. Some agencies claim to be able to name stars on payment of a sum of money. These agencies have no status - have nothing to do with them!

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