George Greenstein is a retired professor of astronomy at Amherst College, the author of Quantum Strangeness (a treatise for the general public on quantum mechanics), and the recipient of numerous awards. To learn more about total eclipses — the type that will take place on April 8, 2024 — Manifest reached out to Greenstein for the celestial scoop.
“I never grant interviews,” Greenstein quips. “I’m like J.D. Salinger.” Fortunately, Didi Gluck, our VP, editorial director, had an in with Greenstein: He is her mother’s partner. So he relented. Here is what Gluck learned:
1. A prehistoric being might have been the first creature to see a solar eclipse. As you may know, a total eclipse, like the one that will take place on April 8, occurs when the moon is exactly lined up with the sun, obscuring it fully. “The thing I didn’t appreciate until recently,” Greenstein says, “is that until science came along, you would’ve had to be in just the right place to see the moon totally covering the sun. If you weren’t there, you wouldn’t have known it was happening because no one stares at the sun. So I’m willing to bet that until science came along, most people probably didn’t know that there were eclipses, except those who happened to live where there was total alignment.” In fact, the ancient Babylonians considered eclipses to be evil omens representing a threat to the monarchy. Before a forecast eclipse, they’d simply appoint a stand-in ruler to suffer the gods’ wrath.
2. Then there’s the potato problem. It’s not common knowledge, but the sun has something surrounding it that is almost always invisible, called the corona, the glowing ring you see behind the sun when it is covered during a total eclipse. But there are some mysteries about the corona. One that Greenstein comes back to again and again is that the corona is hotter than the surface of the sun, yet it is heated by the surface of the sun. “It would be as if you put a potato in the oven at 400 degrees, and the potato came out at 500 degrees. We are not sure why that is,” Greenstein says.
3. One of Albert Einstein’s theories was proved during a total eclipse. Einstein predicted that light is bent by gravity. That light falls. But it wasn’t until 1919, when a British astronomer observed the phenomenon during a total solar eclipse, that Einstein’s theory was confirmed. During the eclipse, “astronomers could see stars, but their positions were wrong because the light from the stars was being bent by gravity,” Greenstein explains. The discovery was declared a revolution in science by The Times of London.
4. Someday, total eclipses won’t be so total. Because of complex gravitational forces, the moon is getting farther away from Earth — making it appear smaller. In the future, it will be too small to fully eclipse the sun. By the same token, there was a time when the moon would have appeared so large, it would have covered not just the sun but the corona too.
5. Thank goodness we can travel! Greenstein says that if you confined yourself to one spot on Earth, you would observe a total eclipse only once every several centuries.
6. For peak totality viewing, take an actual peek? Greenstein says it is “totally safe to remove your eclipse-viewing glasses during totality.” With the glasses on, “you’re going to see a thinner and thinner and thinner crescent, and then it will vanish, and you’ll see stars, like you would at night, and a corona. If you leave the glasses on, you’ll be missing one of the greatest sights,” he says. However, a total eclipse lasts only two or three minutes. Once totality is over and the sun starts to emerge, it’s time to put those glasses back on. All experts recommend never staring at a total eclipse without protective eyewear. Without the glasses, “you can permanently destroy your eyesight,” Greenstein adds, and you wouldn’t know it until about 24 hours later.
You have been enlightened — and warned!
