Meet the stars of Orion’s Belt

Published 4:40 pm Thursday, March 5, 2009

On these chilly March evenings, there’s nothing quite as nice as a good belt, something to keep you all warm and toasty. I’m talking hot chocolate, tea or whatever.

Unless we bump into each other at a happy hour somewhere, I can’t offer that kind of a bump, but what I can offer you is another great belt in these late winter skies that’s naturally intoxicating in a celestial way.

I’m talking about Orion’s Belt in the constellation Orion the Hunter. Even if you’ve never really got into stargazing and astronomy up until now, I know you’ve seen it before. 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 bowtie in the southern sky.

Even with the nearly full moon washing out many of the fainter stars, it doesn’t take too much imagination when you look at that shape 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 orange-red star 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.” As I told you in this column a few weeks back, Betelgeuse is simply the biggest thing you’ve ever seen, except for the latest figure for our national debt.

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. Now that’ll be a reality show that even tops “American Idol.”

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. Nowhere else in the sky anywhere in the world will you see a more perfect alignment of stars 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 actually hundreds of light years apart. 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 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. 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 almost 1,400 years to reach Alnilam.

Alnilam is about 30 times the diameter of our sun. It’s a very hot star with temperatures more than 40,000 degree. Our sun, by comparison, is 10,000 degrees at its outer layer.

What really amazes me is that Alnilam kicks out 375,000 times more light than our sun. If it were 14 light years away instead of 1,400 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 over 21 million miles in girth and is even hotter than Alnilam with a temperature of about 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 6 trillion miles. Alnitak’s also a real shiner, with a luminosity of 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 multistar 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, has a surface temperature of nearly 30,000 degrees and is about 900 light years away. Just as with Alnitak, Mintaka is another multiple-star system made up of at least two stars. As the two stars pass in front of each other the combined brightness of the stars we see varies a bit over time.

Another heavenly gem is on the rise to the far lower left of Orion in the low eastern skies, the planet Saturn in the constellation Leo. The chest and head of Leo take on the shape of an unmistakable backward question mark. Saturn is shining just to the lower left of the query mark and is the brightest starlike object in that part of the sky.

This is a great time to check out Saturn through even a small telescope because it’s at its closest distance to Earth in 2009, about 772 million miles away. The disappointing thing about Saturn this year is that it’s lovely thin ring system is turned nearly edge on from our view, so we can’t see much of it. Still, Saturn is worth a look-see through a telescope.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch.”

The Everett Astronomical Society welcomes new members at members.tripod.com/everett_astronomy.