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The hounds of heaven

Even though it’s now officially spring, there’s plenty of winter left in the early evening skies. Part of the beautiful array of winter constellations are the two best-known dog constellations, Canis Major the Big Dog and Canis Minor the Little Dog. They’ve been on the prowl in the southern Marshall sky for many, many winter evenings chasing down of a variety of prey. Before the winter constellations go on their summer vacation get to know the hounds of the heavens!

Like many constellations, these doggies are formally known by their traditional Latin names. Canis is the Latin word for dog, so Canis Major and Minor are the Big and Little Dogs respectively. In Greek and Roman mythology Canis Major and Minor are Orion’s hunting dogs. When the hermit hunter Orion was killed in a fight with a giant Scorpion, his girlfriend Artemis, the goddess of the hunt, placed Orion’s body in the heavens as the constellation we see today. She also placed his pet rabbit Lepus and his hunting dogs Canis Major and Minor up in the sky to keep him company.

Canis Major is standing on his hind legs to Orion’s lower left in the southwestern sky. The brightest star in the entire night sky, Sirius, known as the dog star, is perched on the Big Dog’s nose. Just extend a line to the lower left using the three bright stars in a row that make up Orion’s belt and you’ll run right into Sirius. Sirius is so bright in the sky because it’s so close to us, only about eight light-years or 50 trillion miles from Earth. It’s about 2 million miles in diameter, more than twice the diameter of our sun.

Right next to Sirius is the star dryly dubbed by astronomers as Sirius B. It has a much more fun nickname though — “the Pup.” A German astronomer discovered it in the early 1800s. The Pup and Sirius are described as a binary star system. These two stars, separated by somewhere between one and 3 billion miles, are revolving around each other every 50 years or so. About 150 million years ago, Sirius B was no pup at all. It was a much, much more massive star than Sirius. Some astronomers even think that at one time it was five times the diameter of our sun, and so bright it could have cast shadows on Earth in the dark countryside. The problem with behemoths like Sirius B is that they don’t live all that long, ripping through their hydrogen fuel at a reckless rate. Once its fuel was exhausted Sirius B went through a series of steps and eventually lost all of its outer layers leaving only its core. That makes the Pup a white dwarf star, no longer producing energy but remaining very hot. The Pup is estimated to be about the size of the Earth, around 8,000 miles in diameter. Sirius B is much denser and more massive than Earth, though, so much that it’s estimated to have a surface gravity near 300,000 times that of Earth. If you weigh 200 pounds on Earth, you would tip the scales at more than 60 million pounds on the Pup!

To find the rest of Canis Major, look for a star just to the right of Sirius. That’s a star called Mirzam, the front paw of the big dog. Then go back to Sirius and look down and to the left for a distinct triangle of stars that outline the dog’s rear end, tail, and hind leg. The star at the tip of the tail is Aludra, a monster size star more than 100 million miles in diameter and almost 2,000 light-years away! Just one light-year equals about 6 trillion miles! Since it’s so very far away, the light we see from Aludra has been traveling to us since around the time of the first Christmas. If Aludra were as close to us as Sirius, it would be the brightest celestial object in the nighttime sky, maybe even more brilliant than the moon! Whenever you gaze upon a star, keep in mind that two factors, size and distance, determine the brightness of a star. Just because a star is dim doesn’t necessarily mean it’s puny. It could be a monster many light-years away.

The Little Dog, Canis Minor, is tagging along to the upper left of Canis Major. Honestly, it’s a poor excuse for a constellation. All there is to the Little Dog is a bright star called Procyon and a dimmer star just above it. It’s a Chihuahua.

If you have any trouble locating Orion’s hunting companions, you can use one of the great treasures in our winter sky. The “Winter Triangle” is an absolutely perfect triangle cornered by Betelgeuse, Procyon, and Sirius. Betelgeuse is the bright red tinged star at Orion’s armpit.

Take an evening walk with the hounds of the heavens!

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is also the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and at  adventurepublications.net. Contact Mike Lynch at  at  mikewlynch@comcast.net.

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