AP NEWS

Starwatch: The great belt of winter

March 9, 2019

Without a doubt, my favorite constellation in the sky is Orion the Hunter, the absolute king of the nocturnal winter skies.

I’m certainly not alone here. When I ask folks at the beginning of my stargazing/astronomy programs if they can find any constellations, the most common response I get is the Big Dipper. I have to let them down gently, however, because the Big Dipper isn’t one of the 88 human-made constellations seen from Earth. The Big Dipper makes up the rear end and tail of the constellation Ursa Major, the Big Bear.

The second most common response I get from folks is Orion the Hunter, and I think the biggest reason is that the giant constellation is the home of the three stars neatly lined up in a row. You can’t find any other parade of bright stars anywhere else in the celestial dome.

Over the years, cultures from around the world have come up with nicknames for Orion’s belt that have nothing to do with a mighty hermit hunter. It’s been called the staff of St. Peter, one of the Apostles. The stars have also been called the Three Kings that visited the Christ child shortly after he was born in Bethlehem. That makes sense because Orion’s belt starts showing up in the evening night sky in December. Orion’s trio of stars also shows up in the Bible in the Book of Job, “Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion?” (King James Version).

Three’s frame

I’ve also heard Orion’s belt referred to as the Three Amigos, the Three Musketeers, the three blind mice, and even the Three Stooges. Back in November in Waconia, Minnesota, I had a woman come up to me after one of my star programs. She told me that on the farm she was raised on they referred to the stars as Wynken, Blynken, and Nod, characters in a popular old American children’s poem.

This time of year Orion and his famous belt of stars proudly shine almost directly above the southern horizon at the as evening twilight ends. From the lower left to the upper right, the belt stars are named 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 actually hundreds of light-years apart. Their arrangement in our sky from our vantage on planet Earth is purely accidental, or is it?

All three stars are much larger than our sun and are unique in their own ways.

The largest of the trio is Alnilam, an Arabic name that roughly translates to English as “string of pearls.” That certainly seems appropriate. Alnilam is about 26 million miles in diameter, 30 times the diameter of our sun! At 1,976 light-years away, Alnilam is so far that even if you could travel at the speed of light, 186,300 miles a second, it would take you nearly two millennia to arrive at Alnilam. Make sure have a lot of reading material on that journey!

Alnilam’s a very hot star with temperatures over 45,000 degrees. Our sun, by comparison, is 10,000 degrees at its outer layer. What really amazes me is that Alnilam kicks out more than 100,000 times as much light as our sun does! It’s a real shiner for sure! If it were 19 light-years away instead of 1,976 light-years, it would easily be the brightest star in our sky. You’d even see Alnilam brightly in broad daylight!

More than meets the eye

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 powered gas ball is over 21 million miles in girth. It’s surface temperature exceeds 60,000 degrees! Traveling to Alnitak would require a journey of a little over 800 light-years. By the way, just 1 light-year equals almost 6 trillion miles!

Alnitak’s luminosity is 100,000 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, on the upper right hand side of the belt, is about the same size as Alnitak. It has a surface temperature of over 50,000 degrees. and is about 900 light-years away. Just like 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 their combined brightness see does vary slightly over time.

Well that’s it, the three stars that make up Orion’s belt, one of the true jewels of the sky. All three of these stars are different in their sizes, power output, temperature, and more; yet all three stars line up neatly in our sky with nearly identical brightness. Personally I can’t help but think that maybe these three stars aren’t lined just by chance, but maybe by a divine hand.

CELESTIAL HUGGING THIS WEEK: On Sunday and Monday night the new crescent moon will pass by the planet Mars in the western evening sky.