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The Moon passes through the middle of one of the largest “asterisms” in the sky the next couple of nights: the Winter Circle. It contains several of the night sky’s brightest stars. But it’s so spread out that it’s hard to take in all at once.
An asterism is a pattern of stars that forms a distinctive shape or picture. It can be within a single constellation, or it can cross over constellation boundaries. The Winter Circle is in the latter category — it encompasses stars in six constellations. It spans about five times the width of your open hand held at arm’s length.
Tonight, the circle’s hub is close to the lower right of the Moon: Betelgeuse, the orange shoulder of Orion, the hunter. Orion’s other brilliant star, Rigel, forms part of the circle itself. It’s to the lower right of Betelgeuse.
If you go clockwise from there, down at the six o’clock position you’ll come to the Dog Star Sirius, the brightest star in all the night sky. Next up is Procyon, the little dog star, then Pollux and Castor, the twins of Gemini.
The circle sweeps upward from there to bright yellow-orange Capella, in Auriga, the charioteer, and then over to Aldebaran, the eye of Taurus, the bull. Finally, it’s back down to Rigel to complete the circle.
It’s one of the grandest pictures in the night sky — a circle of bright stars that tonight forms a giant ring around the bright gibbous Moon.
Tomorrow: projecting Earth’s equator into the night sky.
Script by Damond Benningfield, Copyright 2014