Winter Hexagon
From Wikipedia, the free encyclopedia
The Winter Hexagon is an asterism involving an imaginary hexagon drawn, during the winter, upon the northern hemisphere's celestial sphere; with its defining vertices at Rigel, Aldebaran, Capella, Pollux/Castor, Procyon, and Sirius. Pollux and Castor are very close (just a few degrees) from each other. On most locations on Earth (except the South Island of New Zealand and the south of Chile and Argentina and further south) this asterism is prominently in the sky from approx. December-March. In the tropics and southern hemisphere this (then called "summer hexagon") can be extended with the bright star Canopus in the south.
An alternate name is the Winter Circle.
Smaller, more regularly shaped, and therefore easier to find, is the Winter Triangle, an approximately equilateral triangle that shares two vertices (Sirius and Procyon) with the larger asterism. The third vertex is Betelgeuse. These three stars are three of the ten brightest objects (as viewed from Earth) outside the Solar system, Sirius being the brightest. Betelgeuse is also particularly easy to locate, being a shoulder of Orion, which assists stargazers in finding the triangle. Once the triangle is located, the larger hexagon may then be found.
Several of the stars in the hexagon may also be found independently of one another by following various lines traced through various stars in Orion. See Orion (constellation) for more on this.
The stars in the hexagon are parts of six constellations. Counter-clockwise around the hexagon, starting with Rigel, these are Orion, Taurus, Auriga, Gemini, Canis Minor, and Canis Major. Thus, a star viewer who has located Orion may use the triangle and the hexagon to find five additional constellations.
