There's a lot of bark and bite in the starry skies as we go into the last month of winter, astronomically speaking, of course. The only dog constellations of the night sky, Canis Major the Big Dog and Canis Minor the Little Dog, have been taking their nightly jaunts across the southern skies for many, many winters now, chasing down celestial squirrels, bunnies and such. Before this winter is over and we turn away from that part of space, let's get to know the hounds of heavens. They're nice, they're bright and they don't bite or mess up your lawn.
Like a lot of constellations, they're formally referred to by their traditional Latin names. Canis is Latin for dog, so canis major and minor are the big and little dog, respectively. They're part of the entourage that travels with the legendary constellation Orion the Hunter.
In fact, according to Greek mythology, Canis Major and Minor are Orion's hunting dogs. When Orion was killed in a fight with a giant Scorpion, his girlfriend Diana, the goddess of the moon, 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 with him.
Big dog
The Big Dog, Canis Major, is up on his hind legs to Orion's lower left. 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 from the three bright belt stars of Orion and you'll run right into Sirius. You should have no problem finding it. Sirius is so bright in the sky because it's so close, only eight light-years or nearly 50 trillion miles from Earth. It's a star about two million miles in diameter, more than twice that of our sun.
Right next Sirius is a star dryly dubbed by astronomers as Sirius B, but has a much more fun nickname of "the Pup." It was first discovered by a German astronomer in the early 1800's. The Pup and Sirius create a binary star system and are separated between one and three billion miles, revolving around each other every fifty years or so.
About 125 million years ago, Sirius B was no pup at all, but rather a much bigger dog than Sirius. In fact, some astronomers estimated that it was five times the diameter of the sun and probably could have cast shadows on Earth in the dark countryside.
The problem with behemoths like Sirius B is that they don't live long, ripping through the hydrogen fuel in their core at a beyond predigious rate. Once the fuel was spent, Sirius B, through a series of steps, lost all the outer layers, leaving it with just a gravitationally shrinking core know as a white dwarf star, no longer producing energy, but remaining very hot. The pup is estimated to be about the size of the Earth at 8,000 miles in diameter.
Sirius A is much denser and more massive than our world, so much so that it's estimated to have a surface gravity more than 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 hind foot is called Aludra, a monster-size star more than 100 million miles in diameter and more than 3,000 light years away. Just one light year equals about 6 trillion (6,000,000,000,000) miles.
In fact, the light we see tonight from Aludra left that star before the year 1000 B.C. If Aludra was as close as Sirius is to Earth, it would easily be the brightest thing in the nighttime sky, even brighter than the moon.
Whenever you gaze upon a star, keep in the mind that the brightness of a star is determined by two factors, size and distance. Just because a star is dim doesn't necessarily mean it's puny. It could be a monster many light-years away.
Little dog
The Little Dog, Canis Minor, is 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! Look for Canis Minor just to the left of Orion.
One of the great treasures of the Shamokin winter sky is the "Winter Triangle." It's made up of the dog stars Sirius and Procyon, and the third star is Betelgeuse, the bright red star at Orion's armpit. It forms an absolute perfect triangle.
Enjoy the celestial dog pound!
(Lynch is an amateur astronomer and author of the book, "Pennsylvania Starwatch.")