What is the Winter Circle?
The asterism known as the “Winter Circle” is a large formation of bright winter stars; a pattern that was first conceived by author Hans Augusto Rey (1898-1977) in his popular sky guide, The Stars – A New Way to See Them. While many star guides refer to this pattern as the “Winter Circle,” the overall pattern looks much more like a hexagon. Maybe it should be called the Winter Hexagon?
Which Stars Make Up The Winter Circle?
While it is not one of the 88 recognized constellations in our night sky, the Winter Circle is an asterism, defined an easily identified pattern of stars, and made up of these stars that are located within other constellations (note the many different colors of the stars):
- Sirius (white) the brightest of all stars, in Canis Major
- Rigel (blue) is in Orion
- Aldebaran (orange), in Taurus, lies above Rigel
- Capella (yellow) in Auriga is at the north end of the hexagon
- Castor (white) one of the heads of the Gemini the Twins
- Pollux (orange) the brightest star in the constellation Gemini the Twins
- Procyon (yellowish-white) of Canis Minor
Inside the “circle” lies the intersection of the Celestial and Galactic Equators. The Celestial Equator is simply the plane of the Earth’s Equator, projected on the sky. The Galactic Equator lies in the plane of rotation of the Milky Way. The two are inclined to each other at 62 degrees. That value, corresponding to the angular difference between Earth’s axis and that of the galaxy, shows how far the Earth is tilted from the galactic viewpoint, and vice versa.
The Winter Circle is so big that it even makes Orion the Mighty Hunter look tiny!
Sometimes on winter nights, the Moon is positioned just right and can be seen in the center of the Winter Circle.
What is the Winter Triangle?
Three bright stars within the giant Winter Circle —Procyon, Sirius, and Betelgeuse —make up another asterism known as the Winter Triangle. Because these are bright stars, you can probably spot it first—expand your view to see the full Winter Circle.