The Big Dipper

One pattern, many names

These seven stars sit in Ursa Major, the great bear, and almost every culture made something of them. Americans see a dipper or a ladle, the British a plough, the French a saucepan, and older English a wagon. It is one of the most recognised shapes in the whole sky, and it is an asterism, a pattern, rather than a constellation in its own right.

Your pointer to the rest of the sky

The two stars at the outer edge of the bowl are called the Pointers. Draw a line straight up from them and it lands on Polaris, the North Star. Follow the curve of the handle the other way instead and you can arc across to Arcturus, the bright star in Boötes, then carry on to Spica. This is the first bit of star-hopping almost everyone ever learns.

A quiet eye test

The middle star of the handle, Mizar, has a fainter companion called Alcor sitting right beside it. Being able to split the two with the naked eye was once used as a simple test of good eyesight.

The shape is slowly falling apart

Here is the honest part. Five of the seven stars are genuinely travelling through space together, a loose family astronomers call the Ursa Major Moving Group. But the two on the ends, the lip of the bowl and the tip of the handle, are drifting the opposite way. So the dipper is quietly deforming. A hundred thousand years ago it did not look like a dipper, and a hundred thousand years from now it will not either. We just happen to live in the short window when these stars line up into something we recognise.