How can I see the Winter Triangle?

By Pete Lawrence

Published: Thursday, 27 January 2022 at 12:00 am

The Winter Triangle is what’s known as an asterism, basically an unofficial pattern in the night sky, and can be seen from December to April. Asterisms can be of any size, and can be contained within a single constellation or span several constellations (as is the case with the Winter Triangle).

The triangle is formed from three bright stars visible in the winter sky; Betelgeuse in Orion the Hunter, Sirius in Canis Major the Great Dog and Procyon in Canis Minor the Little Dog.

Betelgeuse is the red supergiant star that marks the northeast (upper left) corner of Orion’s main pattern. Despite being described as ‘red’, to the naked eye, the star appears to be tinted orange. The centre of Orion is marked by three stars of similar brightness sitting in a line, forming another asterism known as Orion’s Belt. Follow the line of the belt southeast (down and left) and eventually you’ll arrive at Sirius the Dog Star, the brightest nighttime star.

Sirius appears bright because it’s close. At a distance of 8.7 light-years, it’s one of the Sun’s nearer neighbours. For comparison, Betelgeuse is 548 light-years away.

From the UK, Sirius never gets very high in the sky. This causes its light to be affected by low-level atmospheric turbulence and it appears to scintillate (the technical term for twinkle) quite noticeably. It’ll often flash vivid colours too, an effect caused by atmospheric dispersion – light from low-altitude objects passing through our atmosphere and spreading into a spectrum of colour.

The third vertex in the Winter Triangle is Procyon, the main star in the small constellation of Canis Minor, the Little Dog. Locate Procyon by extending the top of Orion from Bellatrix through Betelgeuse, for 3.5 times. When you arrive at that point, look south and the brightest star seen will be Procyon. Now, to visualise the Winter Triangle just join the dots!

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