Orion’s belt shines brightly in winter sky
Published 12:56 pm Friday, February 13, 2015
On these chilly February nights, there’s nothing quite as nice as a good belt, something to make you feel warm and toasty. The winter constellations are plenty intoxicating naturally and they hang over, in a good way, over your head every cloud-free Snohomish County night.
In the winter skies we have a bright stellar belt among the stars — Orion’s belt, in the constellation Orion the Hunter. As soon as it’s dark enough, look for a bright star formation that looks at first glance like either an hourglass or a sideways bow tie almost directly above the southern horizon. All of Orion’s stars are bright, but the very brightest are Rigel, which marks the hunter’s left knee; and Betelgeuse, a bright star that appears orange-red to even the naked eye, that marks Orion’s right armpit. In fact, Betelgeuse is an Arabic name that roughly translates to “armpit of the great one.”
The star Betelgeuse is the biggest thing you’ve ever seen. It’s a dying pulsating star that occasionally bloats out to a diameter of nearly a billion miles. Our own sun is no match in size, at less than a million miles in diameter. Keep an eye on Betelgeuse, because sometime between tonight and the next million years, Betelgeuse will blow itself to smithereens. Don’t miss it, although it will be hard not to. Fortunately it’s over 600 light years away, so when it does explode we won’t get any stellar shrapnel or fallout.
Right in the middle of Orion is the hunter’s calling card, the three stars that neatly line up in a row that make up Orion’s Belt. From the lower left to the upper right are Alnitak, Alnilam, and Mintaka. All three stars are much larger than our sun.
The largest of the trio is Alnilam, an Arabic name that roughly translates to English as “string of pearls”. It’s almost 30 times the diameter of our sun. It’s a very hot star with temperatures well over 40,000 degrees. Our sun, by comparison, is 10,000 degrees at its outer layer. What really amazes me is that Alnilam kicks out nearly 400,000 times more light than our sun. If it were 13 light years away instead of 1,300 light years, it would easily be the brightest star in our sky. You’d even see Alnilam in broad daylight.
Alnitak, on the lower left side of Orion’s belt, is an Arabic name that means “the belt.” It’s the second largest of the three stars. This giant nuclear fusion gas ball is nearly 2 million miles in girth, and is even hotter than Alnilam with a temperature of possibly over 45,000 degrees. Traveling to Alnitak would require a journey of a little over 800 light years. By the way, just one light year equals almost six trillion miles. Alnitak’s also a real shiner, with a luminosity of almost 200,000 times that of our puny little sun. There’s also more than meets the eye when you see Alnitak. It’s actually part of its own little three-star family. Alnitak has two smaller companion stars and all three stars orbit each other. There’s no way you can see Alnitak’s companion stars with the naked eye. Actually, that’s very common in our night sky. A lot of stars that appear as a single star in our sky may actually be part of a multi-star family with all of the stars orbiting each other. If you were on a planet around one of these stars you would have multiple suns in your sky.
Mintaka, at just over 900 light years away, is on the upper-right hand side of the belt. It’s about the same size as Alnitak, and is another very hot star with a surface temperature of possibly over 40,000 degrees. Just as with Alnitak, Mintaka is another multiple star system made up of at least two stars orbiting and eclipsing each other. As the two stars pass in front of each other the combined brightness we see does vary a bit over time.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Stars, a Month by Month Tour of the Constellations” published by Adventure Publications available at bookstores at http://www.adventurepublications.net
