The Decibel - What to know about the upcoming total solar eclipse

Episode Date: April 1, 2024

On April 8, the moon will block out the sun giving many Canadians a chance to witness a total solar eclipse. Cities and towns falling in the path of totality are getting ready for this special day and are expected to experience a big number of visitors.The Globe and Mail’s science reporter Ivan Semeniuk explains the science behind eclipses, what makes the upcoming total eclipse special for Canadians and what are the ways to view it safely.Questions? Comments? Ideas? Email us at [e-mail]

It's breathtaking. Ivan Semenik is the Globe's science reporter. You're enveloped in darkness as the darkest part of the moon's shadow comes tearing across the landscape, covers you for a few minutes. He's recounting an experience from 1979. You look up and you see that black hole in the sky, and around it is this extended sort of brush-like feathery glow. Ivan was witnessing a total solar eclipse, and he was captivated.

And I remember even then someone saying, well, the next one in Canada was in 2024. And to me, in 1979, that seemed like a million years away. And yet here we are. On April 8th, a total solar eclipse will pass over parts of Canada. So today, Ivan is here to tell us about the science behind the eclipse and how you can watch it. I'm Mainika Raman-Wilms, and this is The Decibel from The Globe and Mail. Ivan, great to have you here.

Thank you very much. Great to be here. Okay, so Ivan, if you're in the right part of the country on April 8th this year, and the skies are nice and clear, what are we going to see? So let me start with the fact that the moon has sort of an outer shadow and an inner shadow. When you're in the outer shadow, it means that part of the sun is covered by the moon and you get a partial eclipse. If no one told you that that was happening, you wouldn't even know something was happening. As you get closer and closer to the center point of the eclipse, so kind of the midline of the eclipse, there's an area where the darkest part of the moon's shadow kind of slices across Earth's surface.

That path of totality, that's where you can see the total eclipse. It's when you're on that path, as kind of the sun and the moon pass over, you're sort of in perfect alignment and the sun is completely covered by the moon. That's when you get the effect of the sun disappearing behind the moon completely. You see this glowing corona, the sun's outer atmosphere, kind of emanating from behind the silhouette of the moon. You may see some prominences, which are sort of explosions of gas. I mean, you wouldn't see them moving, but they would be kind of just suspended there in the sun's magnetic field.

They kind of have a ruby red glow, and just that color really stands out. You might see some stars. You see some things that are called shadow bands. This is where you can almost imagine them like ripples in a swimming pool, you know, kind of the rippling effect just before the total eclipse. Sometimes you can see these ripples moving across the ground at your feet. If there are birds, animals around, they tend to react to the sudden darkening. Now, if you're very, very near the path of totality, you will get some darkening. Toronto is a good example. It's right on the edge of the total eclipse.

So Toronto will not get a total eclipse, but it will be dark. It'll be almost like someone's turning down this dimmer switch. If the sky is clear, it'll almost be like theater lighting. There are times where sort of the lighting has almost like a purplish glow. And that's what you see, for example, just before and after a total eclipse. So Toronto would get that. But once you're inside the path of totality, that's when literally it's a day and night difference. Because you're in the full shadow. Because you're in the full shadow

and the sun is totally gone. It's unearthly because you suddenly have that feeling, I think, that you're on a moving ball that's hurtling through space and there are other balls up there and things are lining up and moving and your sense of nature and where you are suddenly expands to encompass the rest of the solar system in a very vivid way. And then it's over. This is very exciting to think about this. So

remind us, how exactly does a total solar eclipse work? What's the science at play? It's the product of an incredible coincidence. The moon and the sun are two very different objects. The moon is a tiny little ball that orbits around us, and the sun is a big giant star, and we orbit around the sun. The sun is 400 times larger than the moon, but it's also 400 times further away. So that works out perfectly because it means that from our point of view, the sun and the moon look to be about the same size in the sky. We all know this. You look at the sun, you look at the moon, they're kind of the same size up there. That's just sheer coincidence. There's no reason why they need to be that way.

So because the moon can usually just cover the sun, you get these very spectacular eclipses. They can happen somewhere in the world, usually about five times a decade. So if you're really dedicated, you could see five or six total eclipses every decade. And some people do that and have, you know, over the course of a lifetime, you could see dozens. So when one happens near you, that tends to be a very rare event and it's something you don't want to miss if you can help it because who knows when there's going to be another one. And certainly in Canada, there won't be another one over populated areas until 2044. So it's 20 years away.

That's over western Canada. So for the Great Lakes area, Quebec, and the Maritimes, this is really the one. Yeah. And so this is a total solar eclipse that we're talking about. And of course, this is only one kind of eclipse because there are other varieties, I guess, in a way here. Can you just remind us what other possibilities there are and how are they different? Sure. So of course, there are lunar eclipses as well. We sometimes know that the moon can be eclipsed. And those are fun to watch. That's where the moon goes through Earth's shadow and we on Earth can see the moon darkening. Those are less rare because wherever you are on Earth, if the moon is in the sky, you see the moon going into that total eclipse. Oh, so it doesn't matter so much in which part

of the world you're in then. Exactly. As long as you're on the half of the earth that's facing the moon at that moment. So people may be familiar with lunar eclipses. It's a more common occurrence. Solar eclipses can also be fairly common if it's partial. Usually kind of the moon skirts by the sun, maybe obscures a part of the sun. So the rare thing is when you get that total version where you're right in the path of totality. There's one other type of eclipse which people may have heard of called an annular eclipse. I want to mention that because there was one seen in Ontario and Quebec in 1994. So an annular eclipse is almost like a total eclipse. The one difference is the moon is a little bit further than average in its orbit around the Earth.

So it's slightly smaller, too small to cover the sun completely. And you get this kind of hula hoop effect where the moon goes in front of the sun, but you can still see some of the sun's surface as an unbroken ring around the moon. Those are cool, but a total eclipse is way cooler. Okay. Yeah. So this is really something else that we're about to experience here. So what are we able to see when a total solar eclipse happens that we aren't normally able to? So if you're standing in the path of totality, if you have a pinhole camera, you know, basically a pinhole, and anything that's a tiny hole, it'll cast shadows that start to project the shape of the eclipse. So for example, you know, a colander like you would use to strain pasta,

you could just let the sun shine through that and look at the little dots on the ground and they'll start to take on the shape of the partially eclipsed sun. It'll go from a kind of a cookie with a bite out of it to something that looks like a narrower and narrower and narrower crescent. So roughly about, I would say, an hour and a bit into the partial eclipse, the sun will become a very, very narrow crescent. And then you'll really start to notice it's getting darker. So you almost have to get the

sun 90% covered before you start to really notice an effect. If you're looking at the sun at that moment, there's an interesting effect where just as the moon starts to cover the sun, the sun becomes this narrowest of crescents. And because the edge of the moon is not perfectly smooth, you know, the moon is a rocky ball. It has mountains and valleys. The mountaintops of the moon will puncture through the crescent sun first. And so the crescent breaks up into like a string of beads. It's called Bailey's beads. These are like little points of sunlight shining through the valleys of the edge of the moon. And then everything will be gone. And you just, and at that point you don't need protective eyewear because the sun is

gone. So you just can look with your own eyes and witness this thing. And I think that's where it really makes an impression. We'll be right back. I wonder, Ivan, what have we learned from this kind of eclipse? Like, is there anything that helps us, I guess, understand the earth or the atmosphere, anything like that that we've learned from observing this? Certainly there have been eclipses in the past that have been extremely important for science.

I mean, going all the way back to ancient times, you know, people were able to start to predict the cycles of eclipses based on kind of the movements of the sun and the moon and how often these things would tend to repeat. So there's sort of an ancient astronomy connection to this. But even more recently, the 1800s, when during an eclipse, the element helium was discovered.

So helium gets its name from Helios, the god of the sun, as a result of being discovered during an eclipse. Maybe even more significant is the eclipse that was used to validate Einstein's theory of general relativity, because Einstein showed that gravity should bend light, because gravity is kind of a warping of space. And that means even rays of light that are traveling through space would be affected by that warp, and they should be redirected by the gravity of a large object. So to test this idea, there was a team of British astronomers led by Sir Arthur Eddington

that famously went to see an eclipse, this was in the 1920s, and looked not at the eclipsed sun, but at stars that were very close to the sun. And they could see that those stars actually had shifted in position by a tiny amount. And it was the shift that was due to the gravity of the sun bending the light of the distant stars. So it became a practical test of relativity. There are other things even now that you can do during eclipses that would otherwise be, it's very difficult to observe the corona very close to the edge of the sun. This is like the edge of the sun, basically. Right, exactly. I mean, spacecraft can do this now. Now that we're in the space age, you can put a satellite up in the sky and it can look at the corona, but it's hard to get

really, really close. So you could kind of block the sun and look at the outer corona, but it's hard to get really, really close to So you could kind of block the sun and look at the outer corona, but it's hard to get really, really close to the edge of the sun unless you have this really super convenient filter of the moon, which is almost exactly the same size as the sun. So there are some scientific investigations that still go on during the eclipse.

And I'm just curious, you said kind of going back historically, like people were able to track that this was something that happened semi-regularly, I guess. That's right. What do we know about that? I think that's just mind-blowing that people were able to do that. And I think it kind of goes hand-in-hand with the agricultural revolution because, you know, you need to have people kind of living in the same place for a long period of time and keeping very, very good records of the stars and anything else that happens in the sky.

You know, and people were doing this for agricultural reasons, for religious reasons. It's interesting. keeping very, very good records of the stars and anything else that happens in the sky. You know, and people were doing this for agricultural reasons, for religious reasons. It's interesting. Solar eclipses have a cycle. Actually, it's sort of an interwoven series of cycles. There's a fairly complex mathematics behind it. But you can imagine these kind of interlocking cycles. So when there's an eclipse, there'll be another one in the same cycle about 18 years later, but the earth will be rotated about a third. So it'll happen in a part of the world that you won't see. The same thing again, 18 years after that. But then 54 years later, you will tend to see another eclipse that's very like the one you saw. So people did start to notice these 54-year intervals. So in a specific region of the Earth kind of every 54 years.

Exactly. So you might ask, well, what about 54 years ago? And in fact, there was a similar total eclipse in the same Saros Cycle 139. It's one that traveled more up the east coast of the U.S. and into Nova Scotia. So that was in 1970. Carly Simon has a song about going to see an eclipse of the sun in Nova Scotia. Taking your jet up to Nova Scotia. Yeah, exactly.

Yeah, yeah. So there was an eclipse in Nova Scotia in 1970. A different one in 72. Nova Scotia was very lucky in the early 70s, but hasn't had one since. So ancient people could see these patterns and they could apply also the geometry of the sun and the moon kind of moving around. From their point of view, it looked like the sun and the moon were moving around the earth, and they could see how these cycles would produce events on a regular basis. All right, so for people who do want to go out and try to see this total solar eclipse on April 8th, Ivan, what exactly is the path that the total part of the solar eclipse will take? I'm happy to go through this for Canadians, and I

encourage everyone to go to the Globe and Mail website where, you know, the story we put up includes a very detailed map of where the path of totality is in different regions of Canada. The big picture is this total eclipse starts in the Pacific Ocean, very far from Canada, you know, kind of in the morning and starts, you know, moving towards North America. It first makes landfall kind of around 11 a.m. local time on the Pacific coast of Mexico around Mazatlan, and then begins to curve northward at that point across mainland Mexico and crossing the border into Texas around noonish or so. So then it works its way across the United States kind of from Texas up through the Mississippi Valley, Illinois, Ohio. And it's at that point where it touches Canada for the first States, kind of from Texas up through the Mississippi Valley, Illinois, Ohio. And it's at that point where it touches Canada for the first time, sort of around 3, 315 local time, you know, along the north shore of Lake Erie, Point Gilead Island. So the most southerly points

of Canada will be among the first places to see the total eclipse. Then all along the north shore of Lake Erie, almost the entire Niagara Peninsula is encapsulated by the path of totality. Then across Lake Ontario and eastern Ontario in places like Kingston, Brockville, Cornwall. It misses Ottawa, but it travels along the St. Lawrence to Montreal. Montreal is just inside the shadow. Toronto is just outside. Montreal is just inside. And then Toronto is just outside. Montreal is just inside. And then all across the eastern townships. Then totality crosses into Maine,

then enters Canada again in New Brunswick, right across the middle of New Brunswick. So Fredericton is in the shadow. Miramichi is in the shadow. The western part of PEI from Summerside West is in the shadow. A tiny little tip of Cape Breton Island is in the shadow. And then a large chunk of the island of Newfoundland from Hortobasque to Bonavista. St. John's, Newfoundland is just outside the shadow. But it's a lot of places in Canada. We'll see the total eclipse. Yeah, a lot of people are near that stretch. Either in or near it. Yeah, and we'll have a link in our show notes that links to the map we have of the Global Mail, which actually says the time too, right, that the eclipse will be passing through those areas.

Ivan, though, what happens if it turns out to be an overcast day? Like what if there's clouds in the sky that are blocking it? Then there will be many sad people because, you know, everyone is hoping for clear skies. But we have to face reality. April is not the sunniest month in Canada. And as you go further north and east, it tends to be less and less sunny. Everywhere along the path of the eclipse, there's some possibility that it could be cloudy. Even Texas, where many people are going and where the odds of a clear sky are highest. Just as an example, last year on the same day, April 8th, the Great Lakes area and most of the track of the eclipse in Canada was quite clear. And Texas was cloudy. So there's a

better than 50% chance that in most of Canada, where the path of the eclipse is, will be cloudy at least part of the day. So the question will be which part and how much cloud? And will there be any major weather systems? You know, it's kind of been an unusually warm spring. You know, will that kind of help give us some sunnier skies than average for an April Monday? All of those are sort of open questions. And of course, we know we're not supposed to look directly at the solar eclipse. How can we safely watch it then? So the partial eclipse, you really need, if you're going to look directly at the sun, you need to have protection. So the easiest way is to get a hold of these special eclipse viewers.

And the important thing here is to make sure that they are approved. There's an ISO standard that will be printed on the viewers. There are many things you shouldn't use. Don't use sunglasses. Even if you take a bunch of sunglasses and pile them together, that's not sufficient protection. What you're protecting yourself from is not the brightness of the sun, but other wavelengths that your eye cannot see, which can damage your retina. And you won't feel that damage right away. You might not even notice it until long after the eclipse.

So it's important to not use homemade methods and definitely don't use a mirror, for example, that sort of thing. So while the eclipse is partial, while the sun is only partly covered by the moon, you need to either look indirectly or to have some protection. If you're in the total eclipse for the few minutes that the sun is totally blocked, you can observe safely the sun's corona, the dark silhouette of the moon, the other effects that are happening in the sky, because at that point, the sun is perfectly hidden. Evan, you've talked about how incredible it was to witness a total solar eclipse. I guess, why do you think seeing one has such an effect on people?

It's just such a rare event. So at first you have that. It's extremely rare to see this. And then it's also extremely brief. So you have that sense that this is fleeting. Maybe you've been thinking about it for years and hoping and planning. And then really totality at the most is going to be a few minutes. But I think all of these optical effects, it just makes your hair stand on end. It's hard to explain. You realize you're looking at something very big, kind of profound happening. It is just a part of nature.

I think it just gives you a larger perspective about Earth as a planet and how it fits in with the rest of the solar system and by extension the rest of the universe. Ivan, thank you so much for being here today. My pleasure. That's it for today. I'm Mainika Raman-Wells.

This episode was produced by our intern, Manjot Singh. Our producers are Madeline White, Cheryl Sutherland, and Rachel Levy-McLaughlin. David Crosby edits the show. Adrian Chung is our senior producer, and Angela Pachenza is our executive editor. Thanks so much for listening, and I'll talk to you tomorrow.