Mike Lynch’s Skywatch: Let us ponder the wonder of the great Orion Nebula

7February 2021

The word “awesome” has become a staple of our vocabulary, and that’s great — or should I say awesome? Forgive me if I sound like a curmudgeon, but the downside is that awesome has been watered down. It used to be reserved for truly extraordinary things. One of those things, in my book, is the Orion Nebula in the constellation Orion the Hunter. Even if you view it with just a small telescope or binoculars I believe you’ll agree with me.

Diagram courtesy of Mike Lynch

The most familiar pattern of stars in the night sky is the Big Dipper that makes up the rear end and tail of the large constellation Ursa Major, the Big Bear. In second place, for most folks, is Orion the Hunter. It’s loaded with bright stars, but without a doubt Orion’s calling card is its three stars, evenly spaced, lined up neatly in a row. These are the stars Alnitak, Alnilam, and Mintaka, that outline Orion’s belt. Above them are the two bright stars Betelgeuse and Bellatrix, marking the extent of the hunter’s broad shoulders. Two bright stars below Orion, Saiph and the really bright star Rigel mark Orion’s feet.

Below Orion’s belt, you can’t help but notice three more evenly spaced stars in a row that aren’t quite as bright as the belt but are still relatively easy to see. That’s the great hunter’s sword. If you look at those three sword stars more closely, though, you’ll notice that the middle star is fuzzy. That’s because it’s not a star but what astronomers call a nebula.

Nebulae are enormous clouds of mainly hydrogen gas and dust. Some are laced with heavy elements ejected from exploded stars in the vicinity. They’re also the birthplace of stars. Thousands of stars have already been gravitationally born from the Orion Nebula, and many more are in the making. With a small telescope you can see four recently born stars arranged in a lopsided trapezoid. Astronomers cleverly call it the Trapezium. Even though these stars have been “recently” born, they can still be hundreds of thousands of years old. The Trapezium stars and others are extremely energetic, and the radiation emanating from them is lighting up the nebula like a fluorescent light. Because of this, astronomers characterize the Orion Nebula as an emission nebula.

Even though the Orion Nebula looks small through a backyard telescope or binoculars, it’s anything but! It spans over 30 light-years in diameter. Just one light-year equals nearly 6 trillion miles. It would take over 20,000 of our home solar system lined up end-to-end to span the nebula’s diameter! It looks so small through a telescope because it’s over 1,500 light-years away. Since a light-year is defined as the distance light can travel in one year, we’re seeing the Orion Nebula not as it is now, but as it was sometime before 500 A.D. I can pretty much guarantee that it hasn’t changed all that much.

If seeing conditions are just right and your telescope is powerful enough, the Orion Nebula may have a greenish glow to it. If you’ve seen celestial photos of the nebula, you’ll see many more colors. Don’t blame your telescope for not seeing these colors. Blame your eyes and the distance of the nebula. Our eyes are most sensitive to the color green, and because the light levels from the nebula are so low, our eyes can’t pick much up more than the green component of the light. If we could accumulate light from whatever we’re observing, we would see much more color. Our brains and eyes aren’t wired for that, but cameras are. They can accumulate a lot of light, depending on how sophisticated they are. With many cameras, you can take multi-second or even longer exposures. There are apps for smartphones that make it possible to take multi-second pictures with the camera on your phone. Just for the heck of it, try to take a two- to three-second exposure picture of the Orion Nebula through the eyepiece on your telescope. It’s not easy to do! If you succeed, the image you get of the nebula will be very fuzzy, but you will see more color!

There are certainly other emission nebulae in the night sky throughout the year, but for my money, the Orion nebula is the absolute best!

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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