The "Winter Circle" or "Winter Hexagon" is a bright asterism that's best seen during the months from December to March. The group consists of a large circle of stars or more actually a hexagon shape loosely centred on red supergiant Betelgeuse (mag. +0.42). All stars are bright. Starting from the most northerly point and moving in a clockwise direction they are as follows: Capella (mag. +0.1), Aldebaran (mag. +0.9), Rigel (mag. +0.1), Sirius (mag. -1.4), Procyon (mag. +0.3), and Pollux (mag. +1.1). It's possibly the largest of the well-known asterisms.
What is an asterism?
An asterism is a recognised pattern of stars in the night sky. It may be part of one of the 88 official constellations or it may be composed of stars from many constellations. Anyone can make his or her own asterism and if many people use it often enough it can find its way into Astronomy vocabulary. In the case of the Winter Circle it's no accident it's so large, the six stars come from six different constellations (Auriga, Taurus, Orion, Canis Major, Canis Minor and Gemini).
The Winter Circle is so named because it appears above the southern horizon during the dark Northern Hemisphere winter nights, although it can actually be seen from all over the World. The exceptions are far southerly locations such as the South Island of New Zealand and the south of Chile and Argentina. At tropical latitudes the asterism is visible almost overhead. From southern locations it's towards the northern part of the sky appearing inverted to the Northern Hemisphere view. From the Southern Hemisphere it's called the "Summer Circle" as Summer time is in swing at the time of year.