We’ve gained two hours of daylight since the winter solstice. By February’s end the sun sets around 6 p.m. instead of half past 4, and the sky doesn’t get dark till nearly 8. Hard to believe, but Daylight Saving Time begins in two weeks. We’re in that late winter seasonal transition when one day is sunny and the fine and the next blustery and biting.
Stars are also stirring. I notice that Orion no longer stands due south at nightfall but rather west of south. In a month, the great hunter will tip over on his side and bow out, his round finished for now. With Orion’s slow departure west, a new constellation now rivets our gaze in the southern sky, Canis Major the Great Dog. It seems oddly appropriate that Sirius, the brightest star, should reside in Canis Major — we can’t help focus our attention on its bright beams the same way we might spoil our favorite canine pet.
To find Sirius and from there, the outline of the dog, start with Orion’s Belt and shoot an arrow through it down and to the left. You can’t miss it diamond-like white shimmer; outside of the planet Jupiter and the moon this season, it’s the brightest object in the evening sky. Sirius is brilliant both because it’s close to Earth — just 8.6 light years — and hotter and larger (1.75 times) than the sun. While its name comes from the Greek for “scorching”, it’s most often referred to simply as “the dog star”.
As the brightest star, Sirius has no rival when it comes to twinkling, which is caused by the slipstream of air cells of varying temperature and humidity that the star’s light must pass through before reaching our eyes. Remove the atmosphere and all stars would shine with rock-steady light.
Sirius is flanked on the right (west) by 2nd magnitude Mirzam and on the east by fainter Muliphein. Connect Muliphein with two of its neighbors to form the dog’s head which resembles a collie with a long snout. The front legs and paws are formed from bright Mirzam and several fainter stars nearby. Next, slide south and east to Wezen, which forms a nifty triangle with Aludra and Adhara. Wezen sits at the base of the tail with Aluda at its tip; Adhara and two fainter stars sketch out the hind legs.
In one story from Greek mythology, Canis Major represented the seasoned hunting dog Laelaps, which Zeus gave as a gift to Europa. In another, he’s Orion’s hunting dog. For 21st century skywatchers, the constellation might remind us to feed our pets or take them for their nightly walk. Don’t forget to give your own “Sirius” a scratch behind the ears.