STARGAZING
“Landmarking” Ottawa’s Northern Sky By Brian McCullough
AHHHHH–THE DAY’S ADVENTURE is done. The tent has been pitched and the embers are burning low in the campfire. You lean back and look up to see a thousand points of light sparkling against an inky black sky. Wow! There sure seem to be a heck of a lot of stars up there, far more than you can see from your backyard. Confused? Don’t worry. You’re not the only one who gets “lost in space” under a sky peppered with stars. If you learn to recognize a few of the landmarks, you’ll soon find that navigating your way around the constellations is both fun and easy. Let’s begin by looking at three constellations in the northern sky. With the September equinox well behind us, the crisp, clear evenings of late fall are perfect for getting out to observe the stars. We’re headed north– into bear country!
Ursa Major and Ursa Minor
Once upon a time there were two bears… The ancient Romans called them Ursa Major and Ursa Minor, but most of us know them better as the Great Bear and Little Bear, or Big Dipper and Little Dipper. For Ottawa area outdoor adventurers, these two constellations are well worth knowing. Not only are they the stuff of legends, they are also home to the eight most useful stars in the sky for finding direction–the seven bright stars of the Big Dipper and the North Star in the Little Dipper. The first step is to get oriented. Stand facing roughly north (the spot where the Sun set will be on your left), and search above the horizon for the handle and bowl of the Big Dipper, or Plough, as it is known in Britain. Technically 46
speaking, the two dippers are asterisms, or recognizable patterns of stars in the much larger constellations of Ursa Major and Ursa Minor. According to North American Indian legend, the big and little dippers were long-tailed bears constantly circling the northern sky. Native tribes even used the Big Dipper as a sort of “star clock” based on its position at any given moment during the night. Predictably, the ancient Inuit saw in the Big Dipper a polar bear, forever prowling its ice-cold starry realm. But it is to classical Greek mythology that we must turn for the steamy, R-rated (sex, violence) version of events. Here’s the spin: life is good on Mount Olympus until Hera, wife of the great god Zeus, discovers that her husband has been carrying on a passionate affair with the beautiful maiden Callisto. In a fit of scorn, Hera angrily transforms Callisto into a great bear and banishes her to the forest. (Which goes to show you that even a supreme god like Zeus is no match for a goddess on a mission.) Callisto’s son Arcas, unaware that his mother is now a bear (!), tries to shoot her with an arrow. To save her life, Zeus flings Callisto to safety among the stars to become Ursa Major, and then sends Arcas after her to become Ursa Minor, the Little Bear. You can’t tell from looking, but the
five middle stars of the Big Dipper are moving through space together at an average distance of about 80 light-years from Earth–that’s about 800 trillion kilometres as the crow flies. The stars at each end are actually much further away and moving in the opposite direction. Depending on how sharp your eyesight is, you may detect that the second star in the handle has a much dimmer companion nestled nearby. These two stars are sometimes referred to as the horse and rider. Of course, the real reason we studied the Big Dipper in Cubs and Brownies was to be able to find the North Star–which is still a very handy thing to know when the batteries in your GPS receiver run down. The easiest way to find the North Star (a.k.a. Polaris) is to follow the two “pointer” stars which form the outside of the Big Dipper’s bowl. The North Star marks the end of the handle of the relatively inconspicuous Little Dipper. Contrary to what many people believe, the North Star is not the brightest star in the sky. That honour goes to Sirius in the winter constellation of Orion the Hunter. At a distance of nearly 700 light-years from Earth, the North Star simply doesn’t have the candlepower to make even the list of the top forty brightest visible stars. It’s too bad, really, because the North Star is very useful to us for navigation as it lies–wait for it–almost exactly due north from any point in the northern hemisphere. (Hard luck, mates– there’s no corresponding “South Star” for trekkers in Oz.)
Cassiopeia–Ice Queen of the Milky Way
We leave our two bears now to find the distinctive “W” (or “M”) shaped constellation of Cassiopeia riding high overhead these autumn evenings. Look for it on the opposite side of the North Star to the Big Dipper. The five or six bright stars that form the “W” are line-of-sight dance partners only as they range from about 40 light-years to more than 500 light-years away from Earth. Cassiopeia lies in an area of our Milky Way Galaxy that is rich with stars and well worth exploring with binoculars. If Ottawa Outdoors Fall
