The Winter Circle – or Winter Hexagon – is a big circle of bright stars on the dark dome of night. It’s an asterism, or recognizable star pattern. Asterisms in astronomy are a bit like picking out patterns in clouds; anybody can do it. If a name for a particular pattern is used often enough by enough people, though, it becomes part of the stargazers’ lexicon – as have the names Winter Circle or Winter Hexagon. There’s also a Winter Triangle, a second asterism inside the Circle.
The Winter Circle may well be the largest famous asterism in the heavens. Rigel, Aldebaran, Capella, Procyon, Sirius, Castor and Pollux are the bright stars that make up the large, circular pattern.
When the Northern Hemisphere’s winter solstice arrives on or near December 21, the Winter Circle rises high enough from our northern latitudes to be seen by about 9 p.m. In December, the Winter Circle is highest up in the south around 1 a.m. It appears in the southwest sky around 5 a.m. The western (right) half of the Winter Circle sets in the west before the onset of a winter solstice dawn.
Like all stars, those in the Winter Circle stars rise and set some 4 minutes earlier with each passing night. By late January, the Winter Circle is found in the same places described above, about 2 hours earlier. In late February and early March, the Winter Circle is in your southern sky at nightfall and early evening.
At the center of the Circle, you’ll find center Orion’s bright red star Betelgeuse.
Rigel, the brilliant star below Orion’s Belt, resides at the southwest corner of the Winter Circle.
From Rigel, draw an imaginary line through the three stars of Orion’s Belt to find the southernmost and brightest star of the Winter Circle, Sirius.
The opposite direction through Orion’s Belt points to Aldebaran, the star that depicts the ruddy eye in the constellation Taurus the Bull.
Castor and Pollux, the brightest stars in the constellation Gemini the Twins, are also found by way of Orion’s Belt. A line from the northwest (upper right) star of Orion’s Belt and through Betelgeuse escorts you to these two bright Gemini stars.
Bright Capella, the northernmost star of the Winter Circle, is found to the upper right of Castor and Pollux and the upper left of Aldebaran.
Look for Procyon above Sirius and below Castor and Pollux. Procyon, Sirius and Betelgeuse make up the secondary Winter Triangle asterism, inside the larger Winter Circle.
For some idea of the Winter Circle’s humongous size, an imaginary arc drawn from Sirius to Capella stretches out about one-third the way across the dome of sky.
On a dark and clear moonless night, look for the soft-glowing river of stars that we call the Milky Way to meander right through the Winter Circle.
Bottom line: The Winter Circle is a large circular pattern on the sky’s dome, consisting of the bright stars Rigel, Aldebaran, Capella, Procyon, Sirius, Castor and Pollux.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.