IN NOVEMBER – at least in the part of the northern hemisphere I call home – the nights begin to get darker, the leaves turn all sorts of shades of orange and my dogs’ paws seem to get muddier on every walk. But the one thing that really signals to me that winter is on its way is when Orion appears in the early evening sky.
Orion the hunter is an iconic part of the night sky. Stargazers anywhere in the world can find the constellation using the three stars in the asterism Orion’s belt (pictured). But Orion can also be used to navigate to other parts of the sky. This week, in honour of my two dogs, Peanut and Jack, we will be using Orion to find two constellations named after dogs, Canis Major and Canis Minor. I like to imagine them running along faithfully behind Orion.
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From the northern hemisphere, Orion appears with the red giant Betelgeuse above and left of the belt, and the blue star Rigel below to the right. The dog constellations are to the left of Orion from this orientation. In the southern hemisphere, Orion is the other way up and the dogs are to its right.
Let’s start with Canis Major. This contains the brightest star in the night sky, Sirius. To find Sirius – which is actually a binary star system, not a single star – draw a line along Orion’s belt. In the northern hemisphere, this line goes from right to left, and it is the opposite way in the south. Keep going until you come across a star that appears to twinkle brightly, and you have found Sirius.
All stars seem to twinkle because of the turbulence in Earth’s atmosphere affecting the path of light reaching our eyes. Sirius is the clearest example of this effect. This is partly because it is so bright, but also because it appears low on the horizon in the northern hemisphere, so there is more of the atmosphere for its light to travel through.
Twinkly Sirius makes up the neck of the dog in Canis Major. To find the rest, look below Sirius in the northern hemisphere. You will find a triangle of three stars, which make up the dog’s tail and the top of its back legs.
While Canis Major is quite clearly shaped like a dog, the constellation of Canis Minor requires a lot more imagination. The pattern is made up of two bright stars. To find Canis Minor, you need to use Betelgeuse, Rigel and Sirius. Imagine these stars make up three of the four corners of a parallelogram. Where you imagine the fourth would be, look around that part of the sky for a bright star. That’s Procyon, and once you have it, you have found Canis Minor.
Like Sirius, Procyon is a binary star, comprised of a main sequence star orbited by a white dwarf. Procyon is the eighth brightest star in the night sky because it is quite close to us at only 11.5 light years away, although it isn’t as bright as Sirius, which is “only” 8.6 light years away.
What you need
Clear, dark skies
Binoculars (optional)
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