Opinion Advocates for ideas and draws conclusions based on the author/producer’s interpretation of facts and data.
By Scott Levine
The last time we were together was just after the winter solstice, the very start of winter. Time flies, the world still spins, and as if by magic, we’re about halfway through. There’s already more daylight in late afternoon than there was then.
Changes are happening overhead, too. Back around New Year’s Eve, we talked about looking for Orion and Sirius almost due south at midnight.
Thanks to our ever-moving viewpoint on the galaxy as we keep rolling through our orbit around the sun, we see the stars rise about four minutes earlier each day. That is, any star we look at tonight, will be in that same spot four minutes earlier tomorrow.
Also, we’ll need to look a little farther to the west to find our friends when we look up tomorrow night. This might not sound like much, but just as over enough time water carves the Grand Canyon, those nightly four minutes add up. Sirius is due south now at about 10 o’clock, two hours earlier than it was as the confetti fell.
Let’s start there. Remember, just follow the three stars of Orion’s belt toward the ground. They’ll lead you right to Sirius. Let’s take in its color and see how much it twinkles. Sirius is the brightest star in the entire night sky, and its light travels across over 8.6 light years – that’s around 50 trillion miles – to get to your eye. (A light year is the distance light travels in a year, which means the light from Sirius that we see tonight left for Earth 8.6 years ago.)
If you have a third-grader handy, you can tell them that the Sirius they see tonight is actually Sirius the way it was right around when they were born.
On the grand scale of the galaxy, 8.6 light years is right next door. Sirius is about twice as massive as our sun and doesn’t put out a particularly large amount of energy. Much of the reason it’s so bright in our skies is because it’s so near. Interestingly, though, the part of the sky that it’s in is full of much more luminous stars.
Let’s drop our gaze toward the horizon to find a tidy triangle of three stars. These make up the hind quarters of Sirius’s constellation, Canis Major (the big dog). The brightest of the bunch is Wezen, which is over 1,600 light years away, and Aludra at the triangle’s left-hand corner, is almost 2,000 light years off.
Meanwhile, the stars in Orion’s belt are all many hundreds of light years away, too. Its middle star, Alnilam, is also about 2,000 light years away. I like to imagine where these stars are in real life. They’re not next to Sirius, as they appear, but far behind it, deeper and deeper into the galaxy.
Aludra and Alnilam are among the most distant stars we can see with our unaided eyes, and it’s amazing to think of what must be going on at those stars – how massive and powerful they must be – for us to see them as brightly as we do from so far away.
I hope you take a few minutes to look up and track down these stars this month. Clear skies!
Scott Levine (firstname.lastname@example.org) is an astronomy writer and speaker from Croton-on-Hudson. He is also a member of Westchester Amateur Astronomers, a group dedicated to astronomy outreach in our area. For information about the club including membership, newsletters, upcoming meetings and lectures at Pace University and star parties at Ward Pound Ridge Reservation, visit www.westchesterastronomers.org.
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