How to identify constellations

Being able to recognise the constellations in the night sky can be a lot of fun and also very useful.

From ancient times, mankind has seen patterns in the stars. Getting to know these star patterns can help you feel at home in the night sky and being able to recognise just a couple can help you find many others and help you become familiar with them.

In the past, every culture had its own way of seeing patterns in the stars. These patterns, or constellations, were connected with stories and folk legends. In the west we have settled on a set of constellations largely described by the ancient Greeks with a few more recent additions, and these patterns are used by professional and amateur astronomers alike to describe shapes and positions of stars and objects in the heavens. Each constellation represents a figure in mythology – an animal, bird or object. There are 88 internationally recognised constellations overall. These patterns fall inside a defined box or area and divide up the whole of the night sky. Depending on where you live you may be able to see many but probably not all of them. In the northern hemisphere, for example, you probably won’t be able to see constellations such as Octans the Octant or Pavo the Peacock. Likewise, if you live south of the equator you probably wouldn’t recognise Ursa Major.

Often the brightest stars in a constellation will have names, such as Betelgeuse in Orion or Regulus in Leo. You can use a whole constellation, part of it or even just a couple of known stars to point yourself to another, perhaps less familiar pattern. Some star patterns aren’t constellations in the strict definition of the word and are known as asterisms, but are easily recognised and very useful. The Plough, or Big Dipper, in the Ursa Major constellation is an asterism which can be used to navigate to other constellations. For example, you can use the two end stars in the bowl of the Plough or Big Dipper to point you towards the Pole Star, Polaris, in Ursa Minor. You can use the handle of the Plough to find the star Arcturus in Boötes the Herdsman and follow this line down to the star Spica in Virgo the Virgin. You can see that by getting to know just a couple of these constellations, they can act as stepping stones to finding your way around the rest of the night sky.


Southern hemisphere

January is the best time to view the constellation of Carina the Keel with its bright star Canopus high in the south. Carina is the keel of the great ship Argo Navis – once the largest constellation in the sky. Nearby you’ll find Puppis the Poop Deck and Vela the Sail, all once part of this huge but now disassembled constellation. Canopus itself is the second brightest star in the night sky yet lies around 320 light years away, which means it must be extremely bright.


Southern hemisphere

If you are not familiar with the southern skies, you surely have heard of the constellation of the Southern Cross. You’ll find it riding high in the south in June, the four stars describing a diamond or cross shape in the sky. The brightest star, Alpha Crucis or Acrux, marks the bottom of the cross and is 320 light years away from us. Crux lies in the band of the Milky Way and is surrounded by star clusters and is well worth visiting with binoculars or a small telescope.


Southern hemisphere

May is a great time of year to view the constellation of Centaurus the Centaur. It is quite a large constellation and contains many deep sky wonders such as Omega Centauri, the largest and brightest globular star cluster associated with our Milky Way galaxy. This constellation is also home to the star system of Alpha Centauri, also known as Rigil Kent, the closest star system to our own star the Sun, at just over four light years away. We now know that there are planets in orbit around the stars in this multiple star system.


Northern hemisphere

Sometimes known as the Northern Cross, Cygnus the Swan is a very ancient constellation with several stories attached to it. It rides high in the summer skies in the northern hemisphere and sitting as it does in the band of the Milky Way is full of star clusters and nebulas. The star Albireo, marking the head of the Swan, is a double star. You’ll need a telescope to see this star as a pair, but it is worthwhile as it’s one of the most beautiful doubles in the whole of the night sky, being a lovely contrasting orange and blue.


Northern hemisphere

Orion the Hunter is one of the more easily recognised constellations in the night sky thanks to the three stars of the Hunter’s belt from which hangs his sword. The bright orange supergiant star Betelguese marks the Hunter’s shoulder and the bright white star Rigel, in the opposite corner, his knee. You can use the belt stars as pointers to other stars and constellations. Follow the three stars to the right and you’ll come to the star Aldebaran in Taurus the Bull and left you’ll find Sirius in Canis Major.

Ursa Major

Northern hemisphere

Ursa Major is the constellation in which you can find the Plough or Big Dipper. The seven stars that make up this asterism are the brightest and most easily recognised out of the whole constellation and possibly out of the entire sky. The second star in the handle of the Dipper is a naked eye double star. If you look closely you should see that it consists of two stars very close together. You can use the two stars in the bowl of the Dipper as pointers to Polaris the Pole Star in the constellation of Ursa Minor the Little Bear.

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