High toward the south at around 8 p.m. this week we see 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. Some star guides refer to this pattern as the “Winter Circle,” although the overall pattern looks much more like a 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) and Pollux (orange), the heads of the Gemini 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 waxing gibbous Moon will be passing through the hexagon/circle between February 5th and 7th, though its increasingly bright light will somewhat diminish its prominence as compared to when there is no Moon around to squelch the light of the fainter background stars.