Mike Lynch’s Skywatch: A belt of brightness in the bitter cold

21February 2021

This column is my third and final installment about the constellation Orion the Hunter’s celestial treasures, the best the evening skies have to offer, at least in this stargazer’s opinion. This week I want to highlight Orion’s most conspicuous feature, the three stars evenly spaced in a row depicting Orion’s belt. Even if you’re not all that familiar with the constellation, I know you’ve seen this trio of bright stars in the southeastern sky this time of year.

Before I tell you more about Orion’s brightness belt, I want to make some suggestions about winter stargazing. Of course, the biggest obstacle is the cold. Obviously, you want to dress as warm as you possibly can. If you’re just viewing the constellations, with or without the help of binoculars, I suggest you sit on lawn chairs and cover yourself with blankets. If you’re with that special someone, snuggling really helps! Be prepared to move around your chairs so you can take in the entire sky. I also find that a thermos of hot liquid really helps. If you need a break and have to go into your car or house to warm up, it’s important that you don’t have any lights on inside. You want to maintain your night vision.

If you’re using a telescope, it’s essential to set out your scope and all the eyepieces you’ll be using for a good half hour for the glass in the optics to acclimate together in the cold. Make sure you cover the scope and the eyepieces so they won’t frost up. Once you start observing, it’s also important to keep the lens where light enters your scope free from frost. You can buy special warming strip heaters for this, but you can also use potassium chloride hand warmers. Just attach two or three of them around the outside where the lens is. You can use either duct tape or an oversize rubber band. One more thing, try not to breathe with your mouth when you’re looking through the eyepiece of your scope. It’s very easy to fog over your eyepiece when it’s cold.

Courtesy of Mike Lynch

Once you’re all toasty warm gazing at the constellation Orion, it may remind you of an hourglass or a sideways bowtie. At least it does to me. Unlike many constellations, it doesn’t take too much imagination to see the outline of a broad-shouldered man. All of Orion’s stars are bright, but the very brightest are Rigel, which marks the hunter’s left knee, and Betelgeuse, a bright reddish star that marks Orion’s right armpit.

Between Rigel and Betelgeuse is Orion’s calling card, Orion’s Belt. Nowhere else in the sky from anywhere in the world will you see a more perfect alignment of stars that are this bright. From the lower left to the upper right are Alnitak, Alnilam and Mintaka. You would think that these stars are physically related to each other, but that’s just not the case, not even close! They have nothing to do with each other astronomically. They’re trillions of miles apart from each other. Their arrangement in our sky from our vantage on planet Earth is purely accidental, although sometimes I wonder.

All three stars are much larger than our sun and much more powerful. The largest in the trio is the middle belt star Alnilam, an Arabic name that roughly translates to English as “string of pearls.” That certainly seems appropriate. It’s so far away that even if you could travel at the speed of light, 186,300 miles a second, which Albert Einstein claimed is impossible, it would take you over 2,000 years to reach Alnilam. It’s over 30 times the mass of our sun and is nearly 28 million miles in diameter. Our sun isn’t even a million miles in diameter. It’s a scorching hot star with a surface temperature of around 50,000 degrees F. Our sun, by comparison, is 10,000 degrees F at its outer layer. What really amazes me is that Alnilam kicks out more than 500,000 times more light than our sun. It’s a real shiner, for sure! If it were 20 light-years away instead of around 2,000 light-years, it would easily be the brightest star in our sky. You’d even see Alnilam in broad daylight! By the way, just one light-year, the distance light travels in a year, equals nearly 6 trillion miles!

Located on the lower left side of Orion’s belt, Alnitak is an Arabic name that means “the belt”; it’s the second-largest of the three stars. This giant nuclear fusion gas ball is over 17 million miles in diameter and is even hotter than Alnilam, with a temperature of over 52,000 degrees F. Traveling to Alnitak would require a journey of a little over 1,250 light-years. Alnitak is also really powerful. It has a luminosity around 250,000 times that of our puny little sun. There’s even more than meets the eye when you gaze upon Alnitak. It’s actually part of its own little three-star family. Alnitak has three smaller companion stars, and all four stars orbit each other. There’s no way you can see Alnitak’s companion stars with the naked eye. Multiple star systems like Alnitak’s family are very common in our night sky. Many stars that appear as a single star in our sky are 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!

At about 1,200 light-years away, Mintaka is on the upper right-hand side of the belt. It’s a little smaller than Alnitak but way, way larger than our sun. It’s also a very hot star with a surface temperature over 50,000 degrees F!  Like Alnitak, Mintaka is another multiple star system made up of at least six stars orbiting and eclipsing each other.

Well, that’s it, the three stars that make up Orion’s belt, one of the sky’s real jewels. All three of these stars vary in their sizes, power output, temperature and more, and yet are nearly equally bright and lined up perfectly, at least from our Earthly perch in this part of the Milky Way galaxy. Nowhere else in the night sky will you find a parade of three brighter shiners!

Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private star parties. You can contact him at mikewlynch@comcast.net.

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