THERE are some constellations you only need to learn once, then you can spot them for the rest of your life. Others are more difficult to find, and you might need some help to work out what they are. This week, we are using an example of the former – the mid-sized but distinctive Cassiopeia – as a jumping-off point to explore further.
While Cassiopeia is a northern hemisphere constellation, at this time of year, it can be seen from northern parts of the southern hemisphere too, as far as 20 degrees south. Its position near the north star, also known as Polaris, means it is visible from the northern hemisphere all year.
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Cassiopeia contains five bright stars in a W or M shape, depending on where you are looking from. Of the two upright or inverted Vs that make up the constellation, one is noticeably deeper than the other. To find Cassiopeia, no matter where or when you are looking, a good place to start is by facing north. The constellation won’t be far away.
Cassiopeia is a great constellation to identify on its own, but the lovely thing about it is that it is essentially made up of three arrows that point us towards other objects in the sky.
First, check out the constellations Andromeda and Pegasus. To find them, use the three stars in the deeper of Cassiopeia’s two Vs. If Cassiopeia looks like an M to you, this is on the left, and if it looks like a W, it’s on the right.
Follow an imaginary line from the V’s point, and the line of bright stars that you come to will be the Andromeda constellation. Between Cassiopeia and the first bright star lies the Andromeda galaxy, the closest galaxy to us, which is visible to the naked eye if it is dark enough. Perpendicular to your first imaginary line, away from Cassiopeia, is a large square of stars. This is the Great Square of Pegasus, an asterism that is part of the Pegasus constellation.
Looking in the other direction, and using the middle three stars of Cassiopeia as another arrow, the first constellation you will find is Cepheus. Beyond Cepheus will be the north star, which sits in the constellation Ursa Minor. Looking further still from Ursa Minor, you should see the Plough or the Big Dipper, which is part of Ursa Major.
For a third star-hop from Cassiopeia, draw a line from the middle star to the one to its left if it looks like a W, or to the right if it looks like an M. Keep going and you will get to a line of three stars. This is the top edge of the constellation Perseus.
Go a little further in the same direction and you should see the Pleiades star cluster, a tiny group of stars that looks a little like the shape of the Big Dipper. If you have found the Pleiades, you are at the end of Perseus and into the constellation Taurus.
Try these three star-hops next time you have clear skies.
What you need
Clear night skies
A telescope (optional)
Binoculars (optional)
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