Astro Bob: Two-dog night — How to find Canis Major and Canis Minor
Give a pat on the head to the two celestial canines who woof-woof at Orion's side. They're out at nightfall all this month and next.
The ancient constellation makers must have loved dogs. How do we know? Of the 88 star patterns, three feature canines. The best known are Canis Major and Canis Minor, Latin for the greater and lesser dogs, located within a stone's throw of Orion. Canes Venatici the Hunting Dogs outlines the third pair of hounds, which are tucked under the Big Dipper's Handle. That totals four dogs chasing around the sky, not a bad analogy for what it's like to live in my neighborhood.
To find Canis Major, start at Orion's slanted, three-star Belt. Shoot a line downward through the Belt, and you'll run smack into Sirius, the brightest star in the nighttime sky. A half-dozen fainter but still relatively bright stars (labeled on the map above) shine in its vicinity. The most obvious ones form a nearly-equilateral triangle about one balled fist (10°) below and left of Sirius.
Once you succeed in finding these, branch out to the fainter stars. Use binoculars if necessary. Adding those dimmer suns makes Canis Major one of the few constellations that actually looks like its name. But you'll need a reasonably dark sky to see it.
Before electric lighting, our ancestors took starry nights for granted. Their descendants aren't as fortunate. For many of us a dark sky means traveling. If that's you, use this interactive, light pollution map to identify dark locales in your region. Good skies are colored-coded dark blue, green and gray; the worst are in red and orange. Scroll to zoom in and out, and drag your cursor to move to different parts of the map.
Once you've found Canis Major, Canis Minor will be a piece of cake. Its brightest star, Procyon (PRO-cee-yon), is part of a seasonal asterism called the Winter Triangle, formed by connecting it to Sirius and Betelgeuse in Orion. Procyon is an ancient Greek word meaning "before (pro) the dog (cyon)." It refers to the fact that Procyon rises before Sirius, a.k.a. the Dog Star, for observers in northerly latitudes.
Connect Procyon with 3rd magnitude Gomeisa, located just 4° to its upper right, and just like magic you'll see a petite pup resembling a Yorkshire terrier. Or maybe not. The ancients didn't have much to work with in this part of the sky. Let your imagination fill in the blanks. Gomeisa, Arabic for "the one with bleary eyes," represents the dog's head. But it's also a fitting description for a stargazer after a full night of celestial adventures.
Although Canis Major and Canis Minor are very different constellations their brightest stars, Sirius and Procyon, have several things in common. Both are relatively close to our solar system, with distances of 8.6 light-years and 11.5 light-years, respectively. Procyon is twice the size of the sun and Sirius 1.75 times as big. Each of them is also orbited by a white dwarf, a fantastically dense, tiny star where a cubic inch of matter weighs 15 tons (13.6 metric tons). White dwarfs are what you get when a star with a mass similar to the sun evolves and loses its outer envelope, exposing a super-compressed, Earth-sized core. Think of it as a white-hot coal cooling its heels for (practically) eternity.
"Astro" Bob King is a freelance writer for the Duluth News Tribune.