Answer Man

What would happen if the moon got stuck during an eclipse?

Watch the total solar eclipse in Indonesia in 35 seconds

Members of Slooh watched and captured the total solar eclipse from Indonesia on March 8, 2016. You'll be able to see a similar event this summer here in the metro-east.
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Members of Slooh watched and captured the total solar eclipse from Indonesia on March 8, 2016. You'll be able to see a similar event this summer here in the metro-east.

Q: On Aug. 21, we will be treated to a rare total eclipse of the sun. In fact, for the first time since 1442, one of the best places to enjoy it will be right here in the St. Louis area. My question: What would happen if the total eclipse simply stalled forever at its height? In other words, what would happen if the sun suddenly went away?

Sylvia Hammitt, of Belleville

A: Can you, as Jack Nicholson might ask, handle the truth? Or would you like some Hollywood sugarcoating in which we suspend some trivial matters like, say, the laws of physics? To try to limit your nightmares, Eric Gustafson, educator at the St. Louis Science Center, gave me both scenarios.

Let’s get the worst one out of the way first. If you notice the peak darkness starting to last more than three minutes this summer, all I can say is you’d better be right with your maker. For the eclipse to “stop” would mean that the moon suddenly stopped orbiting the Earth. What would happen next would be like slicing the cables on the elevators at the top of the new World Trade Center in New York. We would begin to see the moon filling more and more of the sky as gravity pulled it crashing into the Earth. Since the moon is about 2,150 miles in diameter, it would make the 6-mile asteroid that supposedly wiped out the dinosaurs 65 million years ago seem like a ping-pong ball by comparison.

The great Isaac Newton proved this three centuries ago, Gustafson said. He imagined what would happen if you shot a cannon on top of an impossibly high mountain. If the cannonball had no acceleration, it would fall to Earth immediately. As you added more acceleration, the farther the cannonball would travel before falling. Eventually, there would come a point where the acceleration would be so great that the cannonball would fall back to Earth continuously but never hit it.

That, in essence, is what the moon currently is doing. It is falling toward earth, but its orbital momentum is so great that it continually misses us. So if the moon suddenly stops moving, gravity is going to pull it headlong into the Earth. Crash! Pow! Ker-blam! as comic book artists would illustrate it. Get ready to send your last text or selfie, because you’d be history in a hurry.

Didn’t like the ending to that movie? Well, then, let’s imagine a science-fiction tale in which the moon somehow can stop in its tracks without slamming into the Earth. So, let’s think about what will be happening that day.

In August, we’ll have the moon coming between the sun and the earth to produce the eclipse. Naturally, those in the shadow of the eclipse will see the sky darkening. This would be particularly dramatic for those in this so-called umbral shadow. For those outside this area of totality, the sky would be similar to what we experience about 40 minutes after sunset. Those in the shadow will notice a drop in temperature, too — perhaps as much as 5 degrees.

But you have to remember that this umbral shadow covers only a small part of the Earth’s surface. Many still will be basking in the sun while we’re oohing and aahing. Temperatures elsewhere will not fluctuate. And while all this is going on, our planet will continue its diurnal and annual motions — meaning that the Earth will continue to spin on its axis (diurnal) as it keeps on truckin’ around the sun (annual).

So what would happen if the eclipse stopped but the moon miraculously remained in the sky? In truth, not much.

“The darkness, temperature and wind changes would occur for a very limited number of people, and the changes would be brief,” Gustafson said. “The brevity of these changes is due to the Earth’s rotational speed of 800 mph near St. Louis. St. Louis would pass through the moon’s umbral shadow very quickly due to the shadow being only 71.2 miles in diameter during (this summer’s) eclipse.

“Once we rotated back to the side facing the sun and moon, the Earth would have shifted a bit in its own orbit. This means the sun, Earth, and moon would no longer be aligned, and the eclipse would be over. The short answer to your question is, not a whole lot would happen if the moon became stuck during the eclipse on Aug. 21.”

This is a radically different question from what would happen if the sun “went away.” If that happened, you may not even want to think about the consequences. It’s the sun’s gravitational pull that keeps the Earth circling it, so we likely would go shooting off into the vast, cold, blackness of space. The planet would retain some heat for a while, but within weeks KTVI’s Dave Murray through chattering teeth would be announcing a new record low temperature of about minus-400 degrees — or 50 degrees above absolute zero, according to the folks at Eventually, only microorganisms would be left thanks to the heat produced at the Earth’s core.

So, hopefully, Annie will continue to be right and the sun will come out Aug. 22, despite some radical religious sects that are predicting the start of the apocalypse again. In the meantime, you can learn more about the eclipse at a free presentation at 7 p.m. June 1 at the McDonnell Planetarium in Forest Park. Admission is free, snacks will be served, and eclipse-viewing glasses will be given away while supplies last. Call 573-884-4482 for information.

Today’s trivia

In what war did Abraham Lincoln and Jefferson Davis wind up as comrades in the service?

Answer to Wednesday’s trivia: In 1917, English King George V decreed from then on “Windsor” not only would be the name of his “House” or dynasty, but also his family’s last name. So, his granddaughter technically is Queen Elizabeth (II) Windsor. However, in 1960, there was a further change when Elizabeth and her husband announced henceforth that their descendants (other than those with a title or women who marry) would carry the name Mountbatten-Windsor.

Roger Schlueter: 618-239-2465, @RogerAnswer