Jimmy Westlake: Winter’s hexagon of stars
January 7, 2013
At about 8 p.m. on cold January evenings, you can spot the Winter Hexagon of stars. It spotlights eight of the 20 brightest stars in Earthly skies — and five of these are in the top 10: Sirius, Capella, Rigel, Procyon and Betelgeuse. The Milky Way slices right through the heart of the Hexagon and it is flanked by two of the sky's most beautiful naked-eye star clusters — the Pleiades cluster leads the way as the Winter Hexagon marches across the heavens, and the Praesepe cluster brings up the rear. This magnificent asterism makes a superb starting point for folks trying to learn their way around the starry sky.
You can locate the first star in the Winter Hexagon by extending a line through the familiar three stars of Orion's belt to the lower left. The flashy star you come to is Sirius, nicknamed the "Dog Star" because it represents the nose of Orion's big hunting dog, Canis Major. Sirius is the brightest and closest of the seven stars in the Winter Hexagon at a distance of only 9 light-years.
From Sirius, shoot a line to the upper right and find the bright blue star that marks the foot of Orion the Hunter, the star Rigel. Rigel looks nearly as bright as Sirius, but is located 100 times farther away at 900 light-years. If Rigel were viewed from the same distance as Sirius, it would shine like a second sun in our sky, being visible in broad daylight.
To the upper right of Rigel is the orange giant star Aldebaran, marking the eye of Taurus the Bull. Aldebaran is 68 light-years away. Its name means "The Follower" because it closely follows the Pleiades star cluster across the sky. The much brighter object beside Aldebaran this winter is the giant planet Jupiter, just passing through.
Continue from Aldebaran by extending a line nearly overhead to the second brightest star in the Winter Hexagon, Capella, a yellow-giant star in the constellation of Auriga, the Charioteer. Capella is a mere 45 light-years away. Although it looks like a single star to the naked eye, astronomers have discovered that it is composed of the light from four different stars.
Dropping down from Capella toward the eastern horizon will lead you to a pair of bright stars — the Gemini Twins, Castor and Pollux. Castor is 52 light-years distant and is not only the fainter of the twins, but is the faintest star in the Winter Hexagon, as well. Pollux is considerably closer to us at 35 light years away.
The Hexagon now continues toward the southeast of the Gemini Twins to the star Procyon. This star's name means "Before the Dog," and it is aptly named because it rises in our sky just before the Dog Star, Sirius, appears. Procyon, like Sirius, is a nearby star, only 11 light-years away.
Close the Winter Hexagon by shooting a line from Procyon back to Sirius where we started.
The eighth star of the Winter Hexagon lies near its center. It is the red supergiant star Betelgeuse that marks the shoulder of Orion. Betelgeuse is very far away, 520 light-years, and is so large that it would fill the orbit of the planet Jupiter if placed in the center of our solar system.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Jimmy's astrophotography website at http://www.jwestlake.com.