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Kousha Navidar: Welcome back to All Of It. I'm Kousha Navidar in for Alison Stewart. We are just about, let's look at the clock, 45 minutes away from the start of today's solar eclipse in our area. You might have heard Brian Lehrer talking with Radio Lab's Molly Webster about it earlier during Brian's show, or maybe during one of our newscasts. You'll be hearing about it right after the show, when we'll be carrying two hours of special coverage of the eclipse from NPR, but just in case you're just tuning in, the moon is about to almost block out the sun. I'm saying almost, but it's a lot. Around New York City we'll be getting about an 87% partial eclipse. If you draw a gently curved line from Dallas, Texas, to Burlington, Vermont, that line, that's the path of totality. Folks closer to that line, we'll see the sun completely disappear from the sky.

Joining us now is Rebecca Boyle, a science journalist with a focus on space and author of the book, OUR MOON: How Earth’s Celestial Companion Transformed the Planet, Guided Evolution, and Made Us Who We Are. She's joining us from inside the path of totality. Rebecca, welcome to All Of It. Do you need a flashlight? How dark is it right now?

Rebecca Boyle: [laughs] Thanks for having me. It's not dark at all, actually, because the partial eclipse is just starting here. I'm in Hot Springs, Arkansas, and we have an incredibly clear sky. We've gotten lucky here unlike a lot of the US today, I think. It's not going to be total here for another hour or so. It just looks like sunlight. As we get closer, it will look a little weird. The light will get metallic and look like it's being filtered through smoky glass maybe, but not until the moment the moon is fully in front of the sun will the sky turn dark.

Kousha Navidar: Listeners, if you've got any questions about the science of the eclipse, we can take those calls. Give us a shout at 212-433-9692. It's 212-433-WNYC. We can take questions about humanity's relationship with eclipses throughout history or questions that you have for Rebecca. Give us a call. 212-433-9692. Rebecca, we've talked a lot about what the eclipse is in previous segments. You just went through it a little bit about what folks can expect. I'd love to talk about the science that it has helped develop because I am really into that part of it. I understand, for instance, that an eclipse helped Sir Isaac Newton prove his theory of gravity. Is that right?

Rebecca Boyle: Yes. Actually, eclipses have been used to prove the two prevailing theories of gravity. The first one is Newton's theory of universal gravitation. His theory broken simply down is that all objects attract one another, and their attraction is proportional to their size, and their distance from each other. In 1715, we had a solar eclipse that was visible across England, actually. It was the first one that Newtonian gravity predicted. It was able to be seen right in that same area where Newton did his work.

Newtonian gravity is the way that people used to predict this event, but Edmund Halley is the one that actually did the math. This is called Halley's Eclipse. He is also the person who predicted the return of the comet that bears his name, Halley's Comet. He didn't live to see either of those actually. He didn't live to see the return of the comet, but he was able to predict this eclipse. It was really close. He was within a few minutes of the forecast of what actually happened, and made a corrective map of the path that the moon's shadow would trace over the Earth. It was a nice confirmation that the gravity is this universal force as Newton had predicted.

Kousha Navidar: What is it about the eclipse that allows big science to be done?

Rebecca Boyle: It's a really unusual thing to be able to see only the atmosphere of our star, and to be able to perceive it in the middle of the day like that without any coronagraph, which is the tech term for an instrument that scientists can use to block the sun's light. It's a really unique opportunity to study not only the sun and the sun's atmosphere, but the Earth's atmosphere, the movement of the moon, the orbit of the moon around the Earth, the movement of the sun across the sky, which means the rotation of the Earth. All of these things can be studied with incredible precision because of this incredible cosmic coincidence of the moon blocking the sun.

Kousha Navidar: Today, is there going to be a lot of experiments, science questions that scientists are going to try to answer? What are some of those questions they're going to tackle today?

Rebecca Boyle: Yes, scientists are really excited about this. Even though it's cloudy, they'll be able to do some really interesting work during the moments of totality, and in the partial phases of the eclipse, which about an hour and a half before and after this four minute phase of totality. NASA is sending up a bunch of sounding rockets into the atmosphere today to look at what happens to some of the clouds, to look at what happens to atmospheric temperatures. There's going to be some interesting studies on the energy grid, actually, because we're moving a lot in the US toward using renewable energy, using solar power, and when the sun is gone for four minutes, that's going to have an effect on the grid. There's some interesting science happening there, too.

There's going to be some constant attention on the sun's atmosphere itself, the corona, which is this beautiful halo of flame that circles the shadow of the moon. That's the part of the sun that reaches out and touches us. The sun illuminates Earth, and is the provider of all life on this planet, but the atmosphere is the way that we directly experience it through the solar wind. It's actually mysterious how it works, and what it does, and how it affects us. This is a great way to see it in real life, in full color. Telescopes around North America are going to be pointed at this event to study the corona in all kinds of detail.

Kousha Navidar: Wow. Listeners, we're talking to Rebecca Boyle, who's a science writer and author of the book, OUR MOON: How Earth’s Celestial Companion Transformed the Planet, Guided Evolution, and Made Us Who We Are. We're talking about the very imminent eclipse that's coming up. We have opened up the phones. If you have questions for us, you can call us or text us. The number is 212-433-9692. Let's go to Steven in Cornwall, New York. Hi, Steven, welcome to the show.

Steven: Hello. Glad to be here. I was wondering, in ancient times, an eclipse was an awesome experience with people. They had no idea about it. Is there any evidence that people had vision problems afterwards, since they didn't know that looking at the eclipse could cause damage to the eyes?

Kousha Navidar: Oh, interesting question. Steven, thank you so much for that. Rebecca, any evidence of that? That seems like something that might be hard to track down, but maybe you know.

Rebecca Boyle: Yes, it would be hard to track down if there are specific instances of people being blinded by the light of an eclipse. It is known that the moon was thought to be involved in curing certain ailments of the skin, actually. People thought that you needed to pray to the moon or use the moon for aid to be able to heal skin problems, things like leprosy back in the Babylonian era, for instance, but honestly, the sun is still so bright during partial phases of the eclipse that it's unlikely that anybody just looked directly at it. You just inherently don't look at the Sun. Even when it's partially eclipsed, it's still so bright.

It's hard to describe how bright the sun is. Obviously, it's the brightest thing that you can imagine, but I think it is really hard to convey how many photons are coming out of that thing, and how every spectrum of light is flowing out of it into your retinas. We have evolved, luckily, to not want to look at that directly and harm ourselves. People probably didn't look at it very long, even in ancient times when they weren't sure what was happening.

During the total phase when the sun is gone, essentially, it's safe to look at the sun directly because it's not there. You're just seeing the corona, and the light of the corona is much more diffused, and much more ghostly looking. It's not going to do any damage to your eyes. There are phases right at the very beginning and right at the very end when you see these phenomena called Baily's beads. This is actually just the sun shining through the craters of the moon and around the mountain valleys of the moon. When you see that, that's when you should look away because it's about to get very bright again. Even a 1% sliver of the sun is so bright that you wouldn't want to look at it directly.

Kousha Navidar: I think this is a perfect time to just put an important notice out to listeners about viewing safety during the eclipse. Like you said, even a small sliver of the sun is very powerful. We did get a call that we unfortunately can't get to from Michelle in Milford. She was asking, "If I don't have glasses, how can I look safely?" Rebecca, break that down for us. What should we avoid doing? What should we do?

Rebecca Boyle: Don't look at the partial phases if you're not in the path of totality. You will burn your retinas, and you will not feel that happening. There are no nerve endings in the retina. It is a nerve cell, but you don't feel the damage, so you would not know if you're causing damage to your sight. You shouldn't look at it directly. What you should do is go out and get a pasta colander or whatever strainer you might have in your house and stand with your back to the sun. Hold the pasta colander over your head or next to your side and look at the shadows that it casts on the ground. Instead of a bunch of dots, you'll see a bunch of crescents. The crescent sun will be on the ground in the shadows. If you're somewhere where the leaves are out on trees yet, just look under the leaves of a tree and you'll see the same thing. There's just a smattering of crescent suns on the ground.

Kousha Navidar: Rebecca, it's almost showtime. Quickly before we let you go, can you talk a bit about how celestial events like the eclipses can have a psychological or emotional impact on us quickly?

Rebecca Boyle: I think it's a really profound experience, and it's a strange thing to witness the sun vanishing being banished from the daytime sky for even just a couple of minutes. It's very eerie and very otherworldly, and even now we know exactly what's happening. We can pinpoint down to the second when this is going to be taking place across the entire continent.

It still is something that's very transformative. People come away from these experiences really changed. In the last eclipse, I was in Paducah, Kentucky in 2017, and there was a crowd of people gathered on the river and there was a little festival and people had music but when it happened, when the shadow of the moon fell on us, this curtain of darkness descended. People were cheering, people were crying, people were hollering and flipping out.

Kousha Navidar: Really impactful it sounds like.

Rebecca Boyle: It's a really profound thing. There are people who are changed by this experience and dedicate themselves to chasing more of them to get that adrenaline rush of the sun vanishing.

Kousha Navidar: We'll have to leave it there. Rebecca Boyle is science writer and author of the book OUR MOON: How Earth Celestial Companion Transformed the Planet, Guided Evolution, and Made Us Who We Are. Enjoy the Eclipse. Rebecca, thank you so much for joining us.

Rebecca Boyle: Thanks for having me.

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