Winter Triangle Puts On A Good Show This Month

Starting with Orion's Belt, we can find our way to the Winter Triangle, Hydra and finally Gemini, located high in the south. This view shows the sky facing southeast around 8:30 in early February. The Triangle will be well-placed for viewing all month. Created with Stellarium

Let’s try to sneak in another constellation hunt before the moon brightens the sky too much. We’ll step outside around 8:30-9 o’clock tonight and face toward the southeast.

By now, most of you are familiar with Orion the Hunter and the three stars that represent his belt. A fist held at arm’s length above and left of the belt will take you to bright, pink-hued Betelgeuse pinned to the hunter’s shoulder. Two fists to the left of Betelgeuse is Procyon, the brightest star in Canis Minor, and two fists below and right of Procyon is Sirius, the brightest star of all.

Together, the three form a nearly perfect equilateral triangle nicknamed the Winter Triangle. You shouldn’t be surprised if it looks a little familiar. The Triangle is part of the much larger Winter Hexagon we visited in an earlier blog.

Hydra the Water Snake is a long, rather faint constellation that straddles both winter and spring skies. Credit (top and below): William Jamiesen/Urania's Mirror

Now that you’ve got the triangle under your belt, draw a line across the top of it to the left or east. As long as the sky is reasonably dark, you’ll run right into the head of Hydra the Water Snake, a compact arrangement of five stars. Dangling below the group is a solitary brighter star called Alphard. Though only 2nd magnitude, or equal to the Big Dipper stars in brightness, its orange color is fairly obvious if you look closely. Can you see it? Alphard is an orange giant star 178 light years from Earth and 50 times the size of the sun.

Hydra is the largest of the 88 constellations and extends considerably farthter to the east and south. We’ll revisit it during spring when more of its stars are above the horizon.

Next we’re off to Gemini the Twins. You’ll find its two brightest stars, Castor and Pollux, by returning to Procyon and looking two fists above it and to the right. Castor is white, while the cooler, redder surface of Pollux makes it look pale orange to the attentive eye. Like Alphard, Pollux is an orange giant.

The mythological twins of the brothers Castor and Pollux make up the constellation Gemini. M35 is bright star cluster above Pollux' feet.

Two swervy lines of stars run approximately parallel to the right and below both Castor and Pollux, forming the main body of the constellation. Or should I say ‘bodies’? Each line represents one of the twins. Their feet turn away from one other at the far western (right) ends. If you look near the tip of Pollux’ foot with binoculars, you’ll see a small,  star-specked cloud called M35. Located 2800 light years away, it’s one of the brightest, easiest star clusters visible in the winter sky.

M35 (left) is a beautiful star cluster in small telescopes and easily visible in binoculars. Larger scopes will show the fainter star cluster NGC 2158 alongide it (right). Photo: Bob King

For reasons I’ve yet to fathom, the Alpha star in Gemini is Castor even though Pollux is clearly the brighter of the two. Did its rank come from position in the constellation or did mom just like him best?

A small telescope will reveal that Castor has a close, bright companion star and a fainter third member. Each of these is double in turn, making for three sets of twins! Pollux gained notoriety recently with the confirmation in 2006 of a Jupiter-sized planet orbiting around it every 590 days. Try picturing these extra goodies in your mind’s eye the next time you gaze up at the twins.