Looking north
Look just above the northern horizon and you’ll see a pattern of stars that will remind you of a large saucepan. This is the famous Plough, or Big Dipper, one of the most easily recognised patterns of stars in the sky – but you might be surprised to learn that it’s not a constellation. The Plough is an asterism, a pattern of stars obvious to the eye that forms part of an actual, larger constellation. The stars of the Plough are part of the constellation Ursa Major, the Great Bear, and represent its hindquarters and tail. Autumn is a very good time of year to see the Plough because it lies parallel to the horizon as darkness falls, and it is in the orientation most people expect it to be.
Mizar and Alcor
If you have reasonably good eyesight and look closely at the star Mizar, (Zeta (z) Ursae Majoris) positioned halfway along the curved handle of the Plough, you’ll see it’s not one star but two, shining very close together. Mizar’s fainter companion is called Alcor (80 Ursae Majoris), and together these two stars are one of the most famous double stars in the whole of the night sky. They were used as a test of eyesight in years gone by. If you can’t split them with your naked eye then don’t worry, as your binoculars will show it.
Polaris
Ask any of your non-astronomer friends to name a star and most will quickly answer the ‘Pole Star’ or ‘North Star’ and a few might even know its official name, Polaris. This is because many people have grown up believing it is the brightest star in the heavens, but this isn’t true. Polaris (Alpha (a) Ursae Minoris) might be the brightest star in Ursa Minor, the Little Bear, but it is only the 48th brightest star
The Plough
in the sky, about as bright as the stars that make up the nearby Plough, so it doesn’t really stand out in the night sky at all. It’s only important because it happens to lie almost directly above the polar axis of Earth, which means all the other stars, their constellations and everything else in the sky appear to rotate around it as Earth spins. Finding it is easy: just go back to the Plough and draw an imaginary line upwards from the two stars known as ‘The
Pointers’ – that line will take you to Polaris.