The Solar Science That Happens During A Total Eclipse
On August 21, thousands of people will line up across the country from Corvallis, Oregon, to Goose Creek, South Carolina, to catch a glimpse of a total solar eclipse. As the moon passes between Earth and the sun and the summer sky briefly goes dark, what will scientists be observing about our nearest star?
Astronomer Shadia Habbal has observed solar eclipses from locales across the globe, including Indonesia, the Faroe Islands, and India. The event provides an opportunity for her to study the temperature of the sun’s atmosphere by using a camera to watch how ions move within the corona.
And astronomer Matt Penn manages the project Citizen CATE (Continental America Telescopic Eclipse), which will coordinate citizen scientists in 60 different locations across the country to snap a panoramic photo of the solar eclipse as it occurs. He’ll use this data to create better models about the velocities of solar winds.
Habbal and Penn discuss the research that will be happening during the eclipse and describe what it’s like to experience sudden darkness in the mid-afternoon.
Science Friday needs your help! We want to mine your eclipse knowledge with this 5-minute survey.
Shadia Habbal is a professor of Astronomy at the University of Hawaii at Manoa in Honolulu, Hawaii.
Matt Penn is an astronomer at the National Solar Observatory and is principal investigator for Citizen CATE. He’s based in Tucson, Arizona.
FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman. I don’t know if you heard, but the place to be on August 21st is Hopkinsville, Kentucky. At exactly 1:24 PM, central time, the sun over Hopkinsville will go dark for exactly two minutes and 45 seconds, and that’s because this summer, the continental US will have its first total solar eclipse in about 40 years.
The path of the eclipse will stretch from the coast of Oregon all the way down to South Carolina, and Hopkinsville will have the longest stretch of darkness. And there is a group of solar scientists who are pretty pumped about this, and that’s because the eclipse is a chance to learn new things about the sun. So while tens of thousands of people will be staring up at the sky this August, solar scientists will be taking photos and even flying through it.
What about you? Are you an eclipse chaser? Do you have a question about what you can see during the solar eclipse? Give us a ring. Our number is 844-724-8255. That’s 844-SCI-TALK. Or tweet us @scifri.
Let me introduce my guest. Shadia Habbal ball is a professor of astronomy at the University of Hawaii at Manoa in Honolulu, Hawaii, and Matt Penn is an astronomer at the National Solar Observatory and principal investigator of the project Citizen CATE. He’s based in Tucson. Welcome to you both.
SHADIA HABBAL: Good morning.
FLORA LICHTMAN: Matt, are you there too?
MATT PENN: Yes, hi, Flora. Thanks for the invitation.
FLORA LICHTMAN: Yeah, thanks for being on. So let’s start with the basics. What do you need, what are the ingredients for a total solar eclipse?
SHADIA HABBAL: So shall I go ahead?
FLORA LICHTMAN: Go for it.
SHADIA HABBAL: So the most important thing is for the moon to totally obscure the disk of the sun, the very bright disk of the sun, so that the outer atmosphere appears. Because the corona, which is the crown of the sun, is a million times fainter than the bright solar disk that we see every day. So that’s why we don’t see the corona. So you really need to obscure it to be able to make the corona come out.
FLORA LICHTMAN: And Matt, we need the moon, basically, to be exactly in line with the sun, is that–
MATT PENN: Yeah, exactly.
FLORA LICHTMAN: Is that a pretty good way to describe it?
MATT PENN: Exactly. And so if you’re thinking about your house, everybody has little specks of dust floating around in their house, and you really can’t see them, normally. But if you have a bright light in a room and you block it out with your thumb, then the light reflects off of that light source, off the dust and into your eye. So the same thing is happening during an eclipse. The sunlight is reflecting off the gas in the atmosphere of the sun and into our telescopes. But we really need the moon to block out the bright source so that we can see it.
FLORA LICHTMAN: I want to get back to the corona in a second, but before we do, I just want to go over some more eclipse basics for people who– citizens who are interested and might see it. I talk to some eclipse chasers for a podcast that I host called Every Little Thing from Gimlet Media about the eclipse experience, and here is how physicist and eclipse chaser Frank Close describes it
FRANK CLOSE: And then, the shadow of the moon is darkness. You see the night sky above you. You can see Venus and a couple of stars. And then as you come down towards the horizon, this dark dome turns into a deep purple, and then a maroon. It looked as if life and energy and everything had been sucked off into the depths of space. In that moment, everything that you take for granted has suddenly gone.
FLORA LICHTMAN: This sounded really intense to me. Matt, is that your experience of seeing an eclipse?
MATT PENN: Some of what you describe is really beautiful, and I think the corona is a really beautiful object in the sky, but when the sun goes away, it’s just wrong. The sun’s not supposed to go away, you know?
FLORA LICHTMAN: It’s scary.
MATT PENN: Yeah, it is. And I like to think of it if you’re a rabbit and the shadow of a hawk passes over you, you know that something’s wrong. You know you’re about to be eaten and you need to run. And maybe that’s a similar feeling that we have as the shadow of the Moon passes over us. We get some sort of primal urge and some realization that this is wrong.
FLORA LICHTMAN: I feel very compelled to see it. Shadia, you are an eclipse chaser yourself.
SHADIA HABBAL: Yes, I do it for science, yes. Yes, for scientific purpose.
FLORA LICHTMAN: How many have you seen?
SHADIA HABBAL: Well I’ve tried to see 14 and we were clouded out by four, so I would say I’ve seen 10 eclipses. And my experience is slightly different. I don’t find it ominous, I just find it awe-inspiring. It’s an incredible sensation when you see the corona appear. I mean, this is what’s so fantastic. All of a sudden, everything dims and then you have this gorgeous aura of lights around the sun that just comes out. And you have the impression that the streams are going out to infinity.
FLORA LICHTMAN: And we can’t usually see that, right? It’s too bright.
SHADIA HABBAL: That’s right. The disk of the sun is way too bright, so you have to block it, as Matt was explaining, to be able to see this outer atmosphere, because the intensity of the disk is a million times more intense than the surrounding corona. So you really need to block it.
FLORA LICHTMAN: And what scientific questions are you interested in about the corona?
SHADIA HABBAL: So what’s puzzling about the corona that was discovered in 1869 also from a total solar eclipse, was the fact that it’s actually a very hot atmosphere. The surface of the sun is around 6,000 degrees. It has dropped from the center where you have nuclear fusion, from 10 million to the surface of 6,000, and then all of a sudden the temperature starts to rise. Now the difference is–
FLORA LICHTMAN: What? Wait, wait, wait.
SHADIA HABBAL: Yes?
FLORA LICHTMAN: It gets hotter as you go–
SHADIA HABBAL: Yes.
FLORA LICHTMAN: –Father away from the center?
SHADIA HABBAL: No. As you go farther away from the surface.
FLORA LICHTMAN: From the surface.
SHADIA HABBAL: So you go from the center to the surface, it drops, and then it starts to go up again.
FLORA LICHTMAN: That’s so puzzling.
SHADIA HABBAL: Yes. So that’s the biggest puzzle, and we’re still trying to figure out what are the processes that are allowing this gas to, all of a sudden, get hot. Now, mind you, that gas is very, very tenuous. So the density is much, much lower than the surface.
So let’s say it’s like sticking your hand in an oven without touching the racks or anything. So you feel the heat, but you really don’t burn yourself. However, because of this very high temperature, you have some elements in the corona, for example.
All the elements you find on earth, iron, chromium, nickel, whatever, they have been stripped of a large number of electrons because it’s so hot. And as they’re losing all these electrons and they get ionized and excited, they emit a certain light of a certain color. So we try to capture this light to be able to get some clues as to what’s causing this hot corona.
FLORA LICHTMAN: So the light you can trace back from the colors that you pick up to understand better basically what’s happening and what chemical processes are happening?
SHADIA HABBAL: Yes, we try to do that. That’s what we– yeah, % that’s what I’m doing.
FLORA LICHTMAN: I saw some– I saw a picture that you created. It was just beautiful, really. That’s a nice and a nice product of the data. It’s really lovely.
SHADIA HABBAL: Thank you.
FLORA LICHTMAN: Matt, tell me about Citizen CATE.
MATT PENN: Oh, yeah. So Citizen CATE is the Citizen Continental America Telescopic Eclipse Experiment, and so now you see why we call it CATE. But the idea is to spread identical telescopes across the entire continent and during the eclipse to take data to look at some science questions. We have volunteers across the country, and they range from middle schoolers through high school up to retired solar physicists who are going to operate the equipment. And then a key part of the experiment is that after the eclipse is over, the various groups get to keep their equipment and continue on with other astronomy projects using that in the future.
FLORA LICHTMAN: And what do you want them to look for?
MATT PENN: So the corona is a mystery, as Shadia was mentioning. One thing that we think as we’re going to see in our data are these polar plumes. So above the north and the south poles of the sun, we expect to see these really thin threads of gas which are constrained by magnetic fields.
So what we know is happening from our observations from space and from the ground is that at the bottom of these plumes, the gas is not really moving very much, but at the top of these plumes, about two solar radii, we know that the gas is moving about 60 miles per second. It’s really flying. This is part of the solar wind. This is a flux of particles that comes from the sun.
FLORA LICHTMAN: I was going to ask, is this the same as solar weather? Is this like a variety of solar weather?
MATT PENN: It’s a type, and you can think of a terrestrial analog. So if a storm comes along on the earth, you need to understand the wind that’s blowing it along to be able to predict where it’s going to hit and what it’s going to do. So the sun emits flares and basically storms in the solar wind, and the solar wind carries it throughout the solar system, and it may impact the earth. So one of our goals is to understand how the solar wind is accelerated, to get some basic understanding about how we can then predict solar weather better, or space weather better.
FLORA LICHTMAN: And citizen scientists will be helping with this effort? That’s so cool.
MATT PENN: It’s a real team effort, and I’m just really enjoying working with a lot of the people. A lot of people, of course, are volunteers, many are students. They’re getting to use some really interesting equipment, and you can tell they’re excited about it. And they’ll get to experience the eclipse as well. And then it’s a win-win. We get a unique data set, as scientists, to understand the eclipse and the processes in the solar wind that we wouldn’t get otherwise.
FLORA LICHTMAN: Let’s go to the phones. Janet in Hillsboro, Virginia, you’re on Science Friday. Do you have a question?
JANET: I do. I’m wondering to be able to look at the eclipse and view the corona, do you need any special viewing equipment? Just get a pair of sunglasses, or just with the naked eye, can you watch it?
MATT PENN: Whoa.
SHADIA HABBAL: Yes.
FLORA LICHTMAN: Go for it.
MATT PENN: Before totality, what you’ll need to use are some special solar viewing glasses. So regular sunglasses won’t work, but when any part of the solar disk is visible, you need a special solar viewing glasses to protect your eyes. But it’s key that when totality happens, that is, when the last bit of that bright sun is covered up, you can take off the solar glasses and just look at the corona with your naked eye. It’s about as bright as a full moon.
FLORA LICHTMAN: Are these things going to sell out? Do we need to get our glasses in order, now?
MATT PENN: Yes.
SHADIA HABBAL: Probably, yes, yes.
FLORA LICHTMAN: Does that answer your question, Janet?
JANET: Where do you buy them? On Amazon, or where can you find glasses like this?
MATT PENN: I think–
SHADIA HABBAL: Rainbow Symphony is one source. It’s a company that sells them. It’s called Rainbow Symphony, so you can look them up online.
FLORA LICHTMAN: For all your solar eclipse needs. Matt, I heard also that you were going to put together a super cut– actually maybe the opposite, a director’s cut– of the eclipse from some of the photos and movies you were getting back from your team of citizen scientists?
MATT PENN: Right, so the idea is that at any one location, like you mentioned in Hopkinsville, you’ll see the corona for about two minutes. But by having a string of telescopes across the country, it will take 90 minutes for the shadow of the moon to move from Oregon to South Carolina. And so if we can stitch together the data from all of our telescopes, we’ll be able to observe the dynamics and the changes in the corona over a 90-minute period of time. So yeah, after the– I’ll be in Idaho, but after the eclipse is over there, I’ll be in a little dark room trying to get data from all of our various sites and stitch it together to form a rough-cut movie that night.
FLORA LICHTMAN: Will I be able to watch it on YouTube?
MATT PENN: Yes.
FLORA LICHTMAN: Shadia, I heard that people would be flying through the eclipse. Can you describe what that’s about, what the goal is, and have you done that?
SHADIA HABBAL: I haven’t personally done it, but in 2015, we had a small group from my team who were on a flight over, close to the Faroe Islands, because the totality also went over the North Atlantic and over the island of Svalbard, so we were on land on Svalbard, but the people who were on the plane got to see it. Of course you’re above the clouds, but then it’s very difficult to collect data because of the very slight vibrations in the aircraft, even though they were reduced with some gyros and whatnot.
But there is a NASA airplane that’s going to fly above the clouds to observe, to collect a spectrum of the sun during totality. And this is to maximize the chances of obtaining observations, because the biggest fear is to have a cloud or to have rain during totality. So when you go in above the clouds, then you maximize your chances, but then it becomes much more expensive because you have to take– make special provisions for the jitter in the aircraft.
FLORA LICHTMAN: I’m Flora Lichtman and this is Science Friday from PRI, Public Radio International. Shadia, can you study the sun by simulating a solar eclipse in the lab or by observing other stars?
SHADIA HABBAL: Simulating, no, you don’t– you can’t do it by simulating in the lab.
FLORA LICHTMAN: I guess I mean could you take a telescope and block out the sun–
SHADIA HABBAL: Oh, yes.
FLORA LICHTMAN: –And look at the corona that way?
SHADIA HABBAL: Yes, yes, of course you do. And this is what’s done in most space-based telescopes that look at the sun and the visible part of the spectrum, those parts that we see with our eye. But the difference between those and the total solar eclipse is that this blocker that they use, which is a man-made blocker, is fairly small, and then it doesn’t– see, the beauty of the eclipses is you start to look at the corona from the solar surface out to several, several solar radii. With a man-made occulter, you are limited to the distance range that you can cover. So sometimes, you lose details that you can only see during a total solar eclipse.
FLORA LICHTMAN: Let’s go to the phones again. JD from Fort Lauderdale, Florida. Welcome to Science Friday.
JD: Yes, hi. I’m an avid listener, first time caller. I’ve got an interesting story. When I was way back in high school, a little solar eclipse in ’71, ’72, I don’t remember exactly what year, I was so enamored with the solar eclipse that came across our little south Georgia town, Hinesville, Georgia, I set up a mirror in the back of my mother and father’s jewelry store and re-broadcasted the sun’s eclipse onto a screen where you could see it. You know, without having to look directly at it.
And again, that’s what made me get all enamored with all things solar, and then later, to become which now, I’m a retired renewable energy executive. But that’s what got me all renewable energy. That’s what made me solar man JD.
FLORA LICHTMAN: Wow!
JD: It was all because of that total eclipse that we got the view in the ’70s, in the early ’70s there in south Georgia.
FLORA LICHTMAN: Oh, wow. Will you be going to see the eclipse this year?
JD: Well, I’m going to do my best to. I’d love to be able to. But I will be watching because I believe the doctor there is going to be doing a live simulcast of his group that’s going to be doing it, so I will definitely be watching the live simulcast. and all of the young children that need to watch it and see it and hopefully some of those minds will work the same way that we have that impressed on me at such a young age to go into all things solar.
FLORA LICHTMAN: I love that idea. Thanks, JD.
FLORA LICHTMAN: Matt, that mirror trick, I’ve never heard of that. Is there any fun things that people can do during the eclipse, or things that people should plan to do during the eclipse?
MATT PENN: Oh, yes, certainly. If you have a pinhole in just a piece of cardboard, you can project an image of the sun onto something and see the crescent during the partial phases, but you don’t really need just the pinhole. During the phases where there’s just a little bit of a crescent left, any shadow looks very strange, so you could hold up your keys and see that they have little crescents where normally they would have straight lines and edges. You could look under trees and see an array of little crescents projected onto the ground, rather than normal sunlight.
FLORA LICHTMAN: We’re going to have to leave it there. We’ve run out of time. I’d like to thank both of you, Shadia Habbal a professor of astronomy at the University of Hawaii at Manoa in Honolulu, and Matt Penn is an astronomer at the National Solar Observatory and principal investigator of the project at Citizen CATE.