Every culture known to history and anthropology has seen in the heavens distinctive patterns, called constellations, and formed by the stars. Constellations are usually comprised of bright stars that appear close to each other. Oriental cultures (the ancient Chinese, for example) formed intricate patterns from some of the faintest stars, creating hundreds of constellations where the West saw only a few. A few constellations, such as Orion, the hunter, and the Great bear represent the same image to widely separated cultures.

So just what are these constellations you keep hearing about? You may go outside some night and see all kinds of stars, and maybe you have even spotted the Southern Cross, but what about Leo the Lion or Pisces the Fish? What are they?

The constellations are totally imaginary things that poets, farmers and astronomers have made up over the past 6,000 years (and probably even more!). The real purpose for the constellations is to help us tell which stars are which, nothing more. On a really dark night, you can see about 1000 to 1500 stars. Trying to tell which is which is hard. The constellations help by breaking up the sky into more manageable bits. They are used as mnemonics, or memory aids. For example, if you spot three bright stars in a row in the winter evening, you might realise, "Oh! That's part of Orion!" Suddenly, the rest of the constellation falls into place and you can declare: "There's Betelgeuse in Orion's left shoulder and Rigel is his foot." And once you recognise Orion, you can remember that Orion's Hunting Dogs are always nearby.

Where did the constellations come from?

OK, so we know the constellations are helpful for remembering the stars, but why would people want to do that (besides an astronomer)? After all, I said at the beginning that farmers invented the constellations. Why did they do that? Was it for some religious purpose?

Yes and no. Around the world, farmers know that for most crops, you plant in the spring and harvest in autumn. But in some regions, there is not much differentiation between the seasons. Since different constellations are visible at different times of the year, you can use them to tell what month it is. For example, Scorpius is only visible in the Northern Hemisphere's evening sky in the summer. When they saw certain constellations, they would know it was time to begin the planting.

When we gaze up into the night sky we see many stars, the planets, the moon, and sometimes a meteor or a comet. If we're very lucky we may witness a supernova once or twice in our lifetime. Over the course of days, weeks and months the planets "wander" among the stars which, while they move nightly across the night sky.

Ancient societies noticed this and believed that some stars had a special significance and associated some patterns of the stars with the goddesses, gods, and stories of their culture. These groups of stars are called Constellations.

In our time, scientists (and most people!) know that the constellations seem to move across the sky because the earth rotates on its axis. What, you may ask, does the turning of the earth have to do with the constellations' motion across the sky? The answer is that the earth moves in a way that makes it look as if the constellations are moving. In the case of the earth and the constellations the earth rotates, with us on it, from west to east. The constellations appear to move from east to west, moving "backwards" from the real rotation of the earth. Actually, instead of saying the constellations rise we should say that the earth has rotated so that we can see different constellations. Then, as the earth continues to rotate the constellations apparently move across the sky. We now know that it is we, on earth that have moved. We know that the part of the earth we are standing on has turned so that the Earth is blocking our view of the stars that have "set".