Planetary Radio • Apr 03, 2024

Syzygy science: Discoveries made during total solar eclipses

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On This Episode

Jeff rich portrait

Jeff Rich

Outreach Coordinator at the Carnegie Science Observatories in Pasadena, CA

Asa stahl portrait

Asa Stahl

Science Editor for The Planetary Society

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

Sarah al ahmed headshot

Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

Planetary Radio marks its last show before the Apr. 8 total solar eclipse with a look back at discoveries made during totality. Planetary Society science editor Asa Stahl shares why solar maximum is excellent for eclipse observing but potentially scary for Earth. Then Jeff Rich, outreach coordinator at the Carnegie Science Observatories in Pasadena, CA, joins Planetary Radio to discuss how total solar eclipses have contributed to our understanding of the Sun and beyond. Bruce Betts, our chief scientist, closes the show with What's Up and a chat about the ways that Einstein's general relativity impacts humanity and our technology.

2017 Total Solar Eclipse
2017 Total Solar Eclipse The total solar eclipse on 21 August 2017 captured the attention of millions as it passed across the United States. This image of the eclipse during totality, taken in Douglas, Wyoming, captures our star's streaming corona in stunning detail. Total solar eclipses provide a unique opportunity to study our Sun's atmosphere without the use of space-based coronagraphs.Image: Blake Estes
Coronal Mass Ejection headed our way
Coronal Mass Ejection headed our way This photo was taken at 01:30 UTC on March 7, about an hour after a coronal mass ejection launched from the surface of the Sun, headed directly torward Earth.Image: NASA / ESA / SOHO
Parker Solar Probe approaches the Sun
Parker Solar Probe approaches the Sun Artist’s impression of Parker Solar Probe approaching the Alfvén critical surface, which marks the end of the solar atmosphere and the beginning of the solar wind. Parker Solar Probe’s crossing into this zone in April 2021 means the spacecraft has touched the Sun for the first time.Image: NASA/Johns Hopkins APL/Ben Smith
The solar spectrum
The solar spectrum Our Sun's spectrum, created from a digital atlas observed with the Fourier Transform Spectrometer at the McMath-Pierce Solar Facility at the National Solar Observatory on Kitt Peak.Image: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF
JWST's First Deep Field Image
JWST's First Deep Field Image JWST's first science image was released a day early, on July 11, 2022, in an address by the President of the United States, Joe Biden. This deep field image is the highest-resolution and deepest infrared view of our Universe taken to date. The light from these galaxies is gravitationally lensed by the mass of the galaxy cluster SMACS 0723 in the foreground. It causes their light to be warped into beautiful arcs. This image shows SMACS 0723 as it was 4.6 billion years ago, but the background galaxies are much further away. The furthest light in this image has taken over 13 billion years to reach us. This image represents a part of the sky that's so small that it could fit behind a grain of sand on the tip of your finger held at arm's length.Image: NASA/ESA/CSA/STScI


Sarah Al-Ahmed: Solar eclipses are a thing of beauty, but they're also a powerful tool for scientific discovery. This week on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society, with more of the human adventure across our Solar System and beyond. The long wait for the next big total solar eclipse in North America is almost over on April 8th, 2024, just five days after the release of this show, a total solar eclipse will sweep across Mexico, the United States and Canada. To mark our last show before our Eclipse-O-Rama Festival in Texas, I'll be speaking with Jeff Rich. He's the outreach coordinator at the Carnegie Science Observatories near our headquarters in Pasadena, California. He joins us to take a look at some of the amazing scientific discoveries that have been made during total Solar eclipses. But first, our science editor, Asa Stahl, will share a little bit about solar maximum and his new article about solar storms. Bruce Betts, our chief scientist, closes out our show with What's Up. We'll take a look at some of the ways that the bending of space-time due to gravity impacts humans and our technology. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it. For people living in North America, there are a lot of reasons to be excited about the April 8th total solar eclipse. Many people across three countries are going to be able to observe a partial solar eclipse, that's when the Moon partially covers the Sun, but tens of millions of people actually live in the path of totality for this eclipse. It's a relatively narrow track across Earth's surface where observers will be able to witness the Moon completely blocking out the Sun. For a few minutes the sky will go dark and the stars and planets will come out, and I promise you, if you have a chance to witness this, it will be one of the most moving experiences of your life. Weather permitting, we're going to be sharing our live stream of the total solar eclipse for everyone from our Eclipse-O-Rama event. We're doing this in partnership with Everyday Astronaut, so if you'd like to watch that live stream, you can tune into everyday Astronaut's channel on YouTube on Monday, April 8th, or you can find that on our website at One of the reasons why I'm personally really excited about this eclipse is its excellent timing relative to the solar cycle, which some people call the sunspot cycle. Our star undergoes this periodic change in its activity and appearance over the course of years from relatively calm at solar minimum to very active at solar maximum. Here's our science editor, Dr. Asa Stahl, with a look at how this solar cycle impacts solar storms and what that can do to people on Earth. ASA's new article, which was published last week is called Should You Be Worried About Solar Storms? Hey, Asa.

Asa Stahl: Hey, how's it going?

Sarah Al-Ahmed: Just so excited for this eclipse. I don't know about you, but it's all I can think about these days

Asa Stahl: Every time I look at the Sun.

Sarah Al-Ahmed: Every time. Or the Moon even. But you just came up with this wonderful article that talks about solar maximum and solar storms and the impacts that those have here on Earth. And as you say in the article, the danger of a major solar storm is now at its highest in over a decade. Why is that?

Asa Stahl: So the Sun operates on an 11 or 22 year cycle, depending on how you want to think about it, such that we have these things called Solar minimum and solar maximum, which are tracking the numbers of sunspots on the Sun's surface that we can see. So this year at some point, we're probably going to hit solar maximum, and we won't know until maybe six months afterward when we see those sunspot numbers decline after the fact. But it seems like that's going to happen this year. And what that means is that solar activity is at its most frequent, the Sun is going to be popping off the most with solar flares and coronal mass ejections and all sorts of things that are scary. They won't be necessarily more intense, but they're just more frequent, and that increases the odds that one of them will hit us. And the reason behind this whole overarching cycle is related to the Sun's global magnetic dynamo, that the Sun has a huge magnetic field because it's full of charge particles moving around in really complex ways, and the geometries of that magnetic field shift over time on a decade-long cycle. And so when we hit this peak this year, it'll be the most active that the Sun has been since 11 years ago when it was last at maximum.

Sarah Al-Ahmed: The tricky bit is that despite knowing that there's going to be more solar activity, we can't really predict with any serious accuracy whether or not there's going to be a solar flare or a coronal mass ejection.

Asa Stahl: Totally. And yeah, it's pretty freaky. I did some research for this article that indicated there were studies that were saying really different numbers of the odds of really intense solar storm hitting us during this solar cycle where one group said maybe 0.1%, which that seems pretty good. I like those odds. And then another group said closer to maybe 12%, 14%, which is uncomfortable. And then another group said maybe 25%, which is scary. So I presented this range of values to Nour Raouafi, the project scientist for the Parker Solar Probe, who I interviewed for the article, and he said, "Yeah, we don't know. The honest answer is We have no idea. But we do know," and this is the part that is concerning, "it's going to happen eventually, probably within the next 50 years. But certainly eventually in the history of modern society, if we still have civilization in the next century, we're going to get hit by one of these storms during that time. It is all but certain."

Sarah Al-Ahmed: What can actually happen to the Earth or say our technological devices if one of these events actually hits our planet?

Asa Stahl: It's a good question and something that is being actively studied, the true answer is we don't know as well. And I think the real impact is going to be the combination of a bunch of different effects that on their own might not be so bad, but altogether could be pretty problematic. So there's a bunch of different things that happen when a major solar storm... And when we say solar storm, there's a few different things that we talk about. We talk about solar flares, we talk about solar energetic particle events, we talk about coronal mass ejections, and these are all slightly different but related things. The thing that we're really concerned about is coronal mass ejection, which is just like a billion ton wave of magnetized plasma, getting flung off the Sun and hitting earth. And if that plasma happens to have its magnetic field basically oriented in a certain direction compared to our magnetic field, then there's magnetic fields sort of scrambles in response. And this causes what's called a geomagnetic storm, and that can do a bunch of different stuff. So when you have that changing magnetic flux in the surface of the Earth, it can induce currents in things like power lines. So if you have long electrical transmission type things, so you get potentially significant blackouts, and it depends a lot on where you are in the world and the geology and how your power grids work and how your transformers are, whether they've been designed to withstand these sorts of things. But there was a report by Lloyds, which is an insurer, I think like an old British insurance company that was saying, "We're concerned about this because we wouldn't have money to pay for all the destruction that would be wrought by a major solar storm," essentially, that if you lose a couple transformers here or there, you might get some blackouts in a couple places that are bad. But then you have replacement transformers come in and it's not so bad, you fix it within weeks maybe. But if a critical number, if you sort of hit critical mass for the number of transformers they're broken, the supply chain to replace a broken transformer is extremely specialized and slow, to the point where it would take years to replace. So the concern being that if a really big solar storm happens and our power grid isn't prepared for, in some places which are especially sensitive, like say the DC to New York metropolitan corridor is one of the worst places apparently in terms of vulnerability for this sort of thing, then that could be really bad. And when you combine that with the fact that GPS systems are also going to lose lock and be degraded in their signaling capability for a while after a solar storm, some satellites could de-orbit because the atmosphere basically produces more drag during a solar storm. This happened, I think it was a year or two ago, but a bunch of SpaceX satellites were on their way up, and then the solar storm hit a relatively minor one, but they were in low Earth orbit and atmospheric drag suddenly increased and they de-orbited, they all crashed back down, which is pretty crazy. And that was just bad timing coupled with a minor storm, but a big storm could also do that. So you have all of that combined with the cables on the ocean floor that connect the internet between continents, that carry internet traffic between continents, they are made of fiber optics. But they have repeaters that are not made of that sort of component to amplify the signal over the massive distances. And those could fail during a solar storm potentially. Pipelines could get corroded or all sorts of things. Basically anything, communication networks, power grids, water pumps for water supplies, railroads, a lot of it is stuff that we don't even think about that depends on... All these different infrastructures are connected. Cell towers rely on GPS, power grids depend on GPS. All these different things can interdepend on one another in ways that lead to cascading failures. And I think the really scary thing is from a disaster relief standpoint is that say you have something massive like Hurricane Katrina, it's terrible in its impact, but it's limited to a geographic area and we can rush supplies to. But this would hit, not just the entire United States at once, but the US and Canada and basically an entire hemisphere of the world at once would be affected, in different ways in different countries, but it would be a massive scale in terms of its spread, and so it'd be really hard to effectively deliver that sort of relief.

Sarah Al-Ahmed: The only answer there is to understand the danger and take mitigating steps ahead of time to make sure that our technology and our infrastructure is robust enough that we can deal with these events. And part of that is making sure that we actually have some understanding of what's going on with the Sun, which is why space missions like Parker Solar Probe as an example, are so important. They're not just telling us more about what's going on with the Sun and its weather, but in real time we're getting more data about these events that then we can use to understand and hopefully prevent some of this damage.

Asa Stahl: Absolutely. Nour Raouafi, the project scientist with Parker Solar Probe, compared our understanding of space weather to that we had of normal weather 50 years ago. We're 50 years behind when it comes to space weather. And our ability to predict the Earth weather just comes down to our ability to understand Earth as a system. It's the same way with the Sun. And yeah, the Sun is really complicated, but we're getting there. Progress is being made, huge strides and incredible missions like the Parker Solar Probe or the Solar Orbiter that just went up, Aditya-L1. We have spacecraft to monitor the Sun and to better understand how these storms form and how they propagate through space to us and how Earth responds to them. All these different sort of steps in the process. But if a storm hit us this year, it would be too little too late. So it all depends on how much we can do, how fast, and so yeah, we need more investment in these sorts of missions. I think the amount of Solar monitoring spacecraft has essentially remained pretty constant over the last 30 years or so. The new ones that have come up have mostly been replacing old ones that have operated for decades beyond their original target, which is incredible that they lasted that long, but also it'd be good to have even more to be able to really understand what the Sun's doing from all angles at all times. But yeah, first the Parker Solar Probe is getting as close to the Sun as anything ever has, is breaking all sorts of records. And it's flown through coronal mass ejections, it's seen firsthand. And then Solar Orbiter is this, I think it's this year, maybe next, it's flying over the Sun's poles and taking close-up images of those areas for the first time. So yeah, literally new looks, new perspectives on our star. But yeah, we have to learn how to live with the Sun,

Sarah Al-Ahmed: And this isn't all just doom and gloom. I mean, I think as an astronomer, someone who spent a lot of time observing the Sun, I'm always really excited for solar maximum when you get all the cool sunspots and all of the cool prominences and stuff that you can see in your telescopes. And we're just a week away, just a few days away from a total solar eclipse. The last one that happened in this area was in 2017, we were near solar minimum. It was a really chill time. But now we're about to have a total solar eclipse in the middle of what is almost a solar maximum. How might that impact what we're going to see during that eclipse?

Asa Stahl: This solar eclipse will look very different than the last one that happened closer to solar minimum for exactly this reason, that when we're at solar maximum, the corona puffs up more. It also has more structure. So we might see prominences or maybe even if we're really lucky, a coronal mass ejection, those take place over the course of hours and totalities only minutes. So you wouldn't see the whole coronal mass ejection happen, but you would see maybe a part of it. Some part of the corona would look like it's detaching off the Sun or a little bubbling type action. Plus, because we're at maximum outside of the corona, we would see during partiality more sunspots on the surface of the Sun. So yeah, it'll be a lot more visually interesting and cool, the Sun will look more like a sort of blossoming flower with petals around it than it would at minimum.

Sarah Al-Ahmed: Beautiful. There's almost no way that we can really predict what will be happening on the Sun that day. So I don't know. It's going to be one of those moments we're all going to... those of us along the path of totality, if we get to see it weather permitting, I guess we'll see all kinds of cool things going on with the corona and then afterwards we can use that to learn more.

Asa Stahl: Yes, I do know that there's a huge number of different official professional solar science projects that are going to be happening during the eclipse and also a lot of citizen science projects to look at the corona and the chromosphere. The two outermost layers of the sun's atmosphere are essentially invisible to the naked eye at any other time except for during a total solar eclipse. So it's like the one time you get to see different parts of the Sun, which is incredible, you'll see the red layer of an outer ring of the chromosphere and then the gossamer strands of the corona further beyond that. And I wonder, I mean, you see images when you watch images taken by spacecraft that block the Sun and essentially do an artificial total solar eclipse. That's how they view the corona, and that's how they watch coronal mass ejections. When you see videos of coronal mass ejections sort of being flung off, that's what it... it look like the same sort of view you'd have with a total solar eclipse. I wonder if we'd be able to see one if it happened during the total solar eclipse?

Sarah Al-Ahmed: I bet we would. That would be so cool. Well, here's hoping the weather actually holds out for us, and I'm looking forward to seeing you at Eclipse-O-Rama in Texas, Asa.

Asa Stahl: Yeah, you too. Yeah, here's fingers crossed for space and Earth weather.

Sarah Al-Ahmed: Oh yeah. Total solar eclipses are the only celestial event that allow humans to observe the sun's corona with the naked eye. The corona is part of the sun's atmosphere naturally. That means that these moments of syzygy, or aligning of celestial bodies, have led to some really amazing scientific discoveries. It's beautiful to think that these moments of totality during total solar eclipses, which lasts just a few minutes at any given location, have acted as such an important catalyst for our understanding of our star and the universe more broadly. To speak about some of the scientific discoveries that have been made during total solar eclipses, we're joined by Dr. Jeff Rich. Jeff is an astronomer and an outreach coordinator at the Carnegie Science Observatories in Pasadena, California. He organizes events for Carnegie, but he also helps create the STEM education program at Mount Wilson Observatory. The history of 20th century astronomy would not be at all the same without the contributions of the Carnegie Observatories in Mount Wilson. These institutions have played such an instrumental role in our understanding of the scale of the universe and our place within it that I really cannot say it enough. Jeff's research focuses on galactic formation and evolution, and he shares his love of space with people every chance he gets, especially during solar eclipses. Hi, Jeff.

Jeff Rich: Hi. Good morning.

Sarah Al-Ahmed: Happy week of the eclipse. Are you so excited?

Jeff Rich: It's hard to contain my excitement. I'm really excited to see the eclipse and excited to share it with as many people as we can. Definitely.

Sarah Al-Ahmed: Have you seen one before?

Jeff Rich: I've been lucky enough to see two eclipses before.

Sarah Al-Ahmed: Wow. Yeah, I've only seen one before, in 2017, but as I was speaking with one of my coworkers earlier on in the show, this is going to be a little different because we're nearing solar maximum, so our opportunities for seeing cool things in the sun's atmosphere might be higher this time.

Jeff Rich: Absolutely. We're talking about that in contrast with the 2017 eclipse. So I'm excited. I get to see it with my own eyes, but for the scientists, really, I think it's going to be an exciting time.

Sarah Al-Ahmed: So we've been talking on this show for weeks now about how this eclipse is this really awe-inspiring moment for everyone. There are tens of millions of people across North America that are going to get to observe this thing, but something that I think we shouldn't understate is the opportunity for scientific discovery because of total solar eclipses. What is it about this situation, specifically during totality, that allows us to really study the Sun in ways that we wouldn't be able to do otherwise, particularly in the past?

Jeff Rich: So one thing that always struck me when I was a graduate student is I had some colleagues who were studying the Sun, they wanted to be solar physicists, and they worked with a professor who would travel to the far-flung corners of the world to take a couple of minutes worth of data every time there was a total solar eclipse. So even before I knew what we could learn, I knew it was something that must be really important that they're going out of their way to go to the middle of the Pacific Ocean or the Libyan desert. The circumstances are that when the Moon completely covers the Sun, you get a chance to study the corona in a way that you can't with all of the other amazing missions and ground-based telescopes that we have that study the Sun, you get a view of the Corona that's really unique and you can see the innermost parts as close to the disk as you can in a way that you can't really see with coronagraphs.

Sarah Al-Ahmed: And that's what's really interesting about it. We have these more modern technologies like coronagraphs that simulate this totality where they block out the Sun so you can study the atmosphere, but it's still not the same, and in a lot of those cases, we have to have telescopes in space to achieve that. So that's a little complicated.

Jeff Rich: The other thing that's really interesting is you and I have been lucky enough to see an eclipse, and hopefully we'll get to see another one next Monday. I feel like not only do the folks who are really interested in collecting data about the Sun during an eclipse, they're going to wherever they can get the most data that they can, but they're also schlepping. They're carrying all this instrumentation with them. They're working really hard to make sure it's working at the last second, make sure nothing's going to go wrong during that crucial time. It sounds so much more stressful than even worrying about whether it's going to be cloudy or not. So it tells me it must be important data to put all that work and effort into getting it.

Sarah Al-Ahmed: I'm glad you brought that up because my experience during the last total solar eclipse was really funny. Most people were asleep. We got there very late because we had changed our eclipse plans because there was a huge forest fire going on in Oregon, so we decided to go to Wyoming instead. And you could see who was there to take data and who wasn't because the people who were there to take data or get astrophotography were literally up at 3:00 AM when we arrived, still tuning their telescopes, still setting up their timers and everything. It must be a really stressful thing to just know that you have these few precious minutes to get this data or your images and just kind of being at the whims of fate as to whether or not the weather is good. So something that was really impressed upon me when I was looking at the eclipse was how clearly you can not only see the Sun's corona, but the magnetic field of the Sun and how that shapes the Sun's atmosphere. And I bet that played a huge role in humanity's initial understanding of the fact that our sun had a solar dynamo to begin with?

Jeff Rich: Absolutely. So I'm lucky enough to work in Southern California, the Carnegie Observatories, where a lot of these discoveries were made, it's something that I didn't really think about until I was working there and visiting Mount Wilson regularly and learning about the history of the fact that we didn't know there were magnetic fields in the Sun or that sunspots were a little bit cooler than the atmosphere around them, is something that we take for granted that took a lot of hard work and observation. I think this is something we come back to when we talk about the work that we're doing now, so the solar physicists who are trying to collect data of the Sun are using cutting edge technology and the stuff that we get to see at a place like Mount Wilson, that it was cutting edge a hundred years ago, making these really big discoveries about the Sun, it's hard to wrap your head around, for me anyway, even though I have it there right in front of me. Sorry, I'm getting off track. That's not solar eclipse related, but.

Sarah Al-Ahmed: But I think something that's really cool about Mount Wilson, and I'm not sure if this is still ongoing, but the study of the Sun at the time early on necessarily meant that we couldn't take great photos of it. We have to draw the sun's atmosphere with sunspots each day, and that's something that Mount Wilson has been doing for quite a long time is this hand-drawn record of what's been going on in the Sun because we need it to be consistent with what was going on before. And I love that Mount Wilson has done that, among the many amazing discoveries that have been made up there.

Jeff Rich: Oh, yeah. And it's still going.

Sarah Al-Ahmed: It is still ongoing, someone's still hand drawing the Sun?

Jeff Rich: Yep. Every morning that they can, they still are drawing the Sun and keeping those data going forward because it's an important record. Which ties into space weather. That's one of the big reasons that we want to understand the Sun, and that has a direct impact on our life here on Earth, especially nowadays with the potential impact to satellite communications and earth-based communications. Anything that helps us understand the Sun as a star better is a plus, a bonus.

Sarah Al-Ahmed: Well, I mean it's so necessary these days. In the past, if you had yourself a Carrington style event, maybe you're going to get some cool aurorae. Maybe you might have some effects in the atmosphere. But now we live in a world where everything is technological based. If we have some giant solar storm coming from space and we don't see it coming, even with all of our understanding, it could deeply impact our technological society. So this is even more important as time goes on.

Jeff Rich: Absolutely.

Sarah Al-Ahmed: Before we move on, because I don't think we've ever really had a chance to speak about this on the show very much, but there have been some major scientific discoveries, particularly in the realm of astronomy that have happened up at Mount Wilson. For people who aren't super familiar with the legacy of that observatory, what are some really cool things about the way that our understanding of the universe has been changed because of that observatory?

Jeff Rich: Oh. Well, I'm a nighttime astronomer, so I look at galaxies and stars, and that's really... The huge discoveries that were made at Mount Wilson were some of our fundamental understanding of the Sun as well as our place in the universe. We really discovered the universe at Mount Wilson. When the first telescopes were built at Mount Wilson, we didn't understand really anything about the Sun. We didn't know our place in the universe. We didn't know that there were galaxies outside of our own. We didn't know where we were in the Milky Way. Within a couple of decades of the completion of the telescopes at Mount Wilson, we went from thinking we were in the center of the Milky Way maybe to knowing that the Milky Way is 100,0000 light-years across, we're nowhere near the middle where out in the suburbs. And then just a few short years later, we went from knowing that the universe is the Milky Way to not knowing how many galaxies there are and knowing that there are galaxies beyond our own. And not only that, that the universe is expanding, that these massive shifts in our understanding of the universe all came from these really important telescopes at Mount Wilson that allowed astronomers to sort of make these measurements for the first time. I really like talking about the discovery of the fact that we're not the only galaxy out there because for a very long time, people were debating and discussing, there was a great debate about whether the spiral nebula were galaxies beyond our own, were stellar systems beyond our own with no evidence. And it reminds me of the really hard work that people are doing to find life on other planets and find planets that might be habitable. There's a lot of work that goes into just discussing how you would even do that, because it really gets people thinking about the work that you would have to do to prove that. I realize I'm getting off track again because that's nighttime astronomy, but there's also a whole laundry list of big discoveries about the Sun, not just the fact that the discoveries were made, but the technology was developed at Mount Wilson to have modern solar telescopes that could actually take the data to observe magnetic fields in the Sun, that they built the first Solar telescope and realized the flaws that it had and thought, how can we make this better? Built another solar telescope, and that made the discovery that there's magnetic fields in the Sun and then built an even better solar telescope that later discovered that the Sun is ringing like a bell, that it's oscillating. These are really building on not just the science, but the technology that we need to support that work. That tradition continues to this day for sure.

Sarah Al-Ahmed: It's really beautiful seeing that progression from the initial hand drawings of the Sun then on to actually taking images on these glass plates and things like that, which Carnegie Observatory, your center here in Pasadena, is just full of these glass plates. And if anybody out there ever wants to go see some of these beautiful pivotally important glass plates in the history of astronomy, highly encourage you to reach out to the people at Carnegie Observatories. But one of the things that I think is a really cool connection here is that Einstein and Hubble, all of those people up at Mount Wilson were a huge part of the legacy of that observatory and total solar eclipses were actually really fundamental in helping us really prove a lot of what they both said. But Einstein in particular, even when I was in university, one of the things that I learned in school was that one of the biggest major discoveries during a total Solar eclipse was actually in 1919 when Sir Arthur Eddington used a total Solar eclipse in order to validate Einstein's theory of general relativity. And before we get too deep into the weeds on that, for people who are unfamiliar, what is general relativity?

Jeff Rich: General relativity is a way of mathematically expressing the relation between space and time and gravity that is a different way of thinking about the relationship between those things. To put it in a really simple terms, if you've ever been to one of those demos at a museum where you stretch a piece of fabric and drop a big ball in the middle, and that ball distorts the fabric and then you can roll marbles around it, that's a two-dimensional representation of what gravity is doing to space and time. The gravitational effect that the mass of stars, the mass of galaxies, just anything that has mass, that mass will distort space in a way that you can use to account for the motions of anything. And it's an advancement on Newtonian dynamics so there's a little bit of extra math in there. And I haven't had to take the math class in a while, so I'm saying all this without having to write these equations down for you because it's not easy. It took Einstein and others who were helping to solve those equations, a lot of work. So I'm glossing over things here, but it's a way of relating gravity and space and time to allow us to account for some inadequacies in Newtonian dynamics that didn't explain some of the things we were seeing. One of the really interesting things about general relativity is it says that light should be bent by mass. Light should be bent by anything that has mass. So the more mass of the object, the more you're going to bend that light. And in 1913, Einstein wrote George Ellery Hale, the director of Mount Wilson, and ask for advice on how to prove this by looking for stars during a solar eclipse. So the idea would be if you want to show that light can be bent by mass, well, the Sun is this nice big mass right next to us, but it's hard to see stars during the day. So if you want to look for a star that's light path is close enough to the Sun and the sky that you can detect that change, that shift, a Solar eclipse might be the perfect time to do that. So this is what Eddington eventually proved was that the gravitational mass of the Sun actually curved the path of light of a star and did it in a way that was predicted using the equations that were set out by general relativity. This is one of the early sort of proofs of those equations. This is something that we've been trying to do over and over again even just a few years ago with the detection of gravitational waves being another proof, a prediction that was made by the equation set up by Einstein that was proved by people working really hard to observe an effect predicted by general relativity.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Jeff Rich after the short break.

Casey Dreier: This is Casey Dreier, the Chief of Space Policy here at The Planetary Society, inviting you to join me, my colleagues, and other members of The Planetary Society this April 28th and 29th in Washington DC for our annual day of action. This is an opportunity for you to meet your members of Congress face-to-face and advocate for space science, for space exploration, and the search for life. Registration closes on April 15th, so do not delay. I so much hope to see you there at our day of action in Washington DC this April 28th and 29th. Learn more at

Bill Nye: The total Solar eclipse is almost here. Join me and The Planetary Society on April 7th and 8th for Eclipse-O-Rama 2024, our can't miss total solar eclipse camping festival in Fredericksburg, Texas. See this rare celestial event with us and experience a whopping four minutes and 24 seconds of totality. The next total solar eclipse like this won't be visible in North America until 2044, so don't miss this wonderful opportunity to experience the Solar System as seen from spaceship Earth. Get your Eclipse-O-Rama 2024 tickets today at

Sarah Al-Ahmed: How completely bonkers is that? I mean, trying to prove general relativity exists is one thing, that's absolutely mind-blowing, and just the idea that they would use a total Solar eclipse in order to do that validation is so clever, but I cannot imagine how much Einstein would lose it over a hundred years later knowing that we could validate something like gravitational waves. I mean, it took the cleverness of everyone trying to build LIGO, the Laser Interferometer Gravitational-Wave Observatory. It is so amazing, and I don't think Einstein even thought it was possible for us to be able to validate that. So it's amazing seeing how far we've come with that.

Jeff Rich: I feel like the story is the same in 1919 and now, it's a lot of people who were really interested in trying to understand the universe. Eddington had to carry all this equipment to a corner of the world to collect the data and the way that we keep talking about, but it would've been no small feat in 1919. But really wanting to try to get that data to try to understand what we think we might know about the universe or might not. The data could have come out a different way, and it's what we keep looking for.

Sarah Al-Ahmed: Where did he have to go to actually do this observation?

Jeff Rich: So Eddington, when he took the data in 1919, he took data from Sobral in Northern Brazil and the island of Principe off the coast of West Africa. So it was a multi-location expedition.

Sarah Al-Ahmed: Well, I mean, I imagine that's a good idea to hedge your bets just in case one location has bad weather, or in case you need some way of verifying the data you took. Because the bending of light around an object like the Sun, even though the Sun is a very massive object, it is a very small effect for a star of that size. It doesn't become super apparent until you're looking at something like say, gravitational lensing around a giant galaxy cluster.

Jeff Rich: Exactly. Exactly. Which now we use that technique regularly to measure the properties of clusters and to exploit the magnification of light through gravitational lensing. It's another thing we just take for granted now that is a really important technique in our observations of the distant universe.

Sarah Al-Ahmed: And it wasn't even that long ago that was a hundred years ago that we began to understand this and finally verify it, and it's become so central to the way we understand the universe and even just our technology. We'll get into that later on in the show talking about how general relativity and even special relativity impacts our technology, particularly our satellites. But as an example, one of the things that total solar eclipses have allowed us to understand is the chemical makeup of the Sun. You'd think you could just point a spectrograph or something at the Sun to try to figure out what it's made of. But for years, I've been telling children during school field trips and outreach events, did you know that we didn't know that helium existed until we were studying the Sun? What I didn't know until I was in full eclipse brain all the time was that that discovery was actually made during a total solar eclipse. Can you talk a little bit about that?

Jeff Rich: Sure. Well, the interesting thing is the discovery of helium is a little bit of a long path because it was discovered, it was first observed during an eclipse, it was observed using a technique called spectroscopy. We use this all the time. I'm sure it's come up on your show before because it's one of the most fundamental techniques for us to help understand the universe, taking light and splitting it into a spectrum and measuring very carefully exactly how much light you're getting in different colors. And there are all these fingerprints that we already knew about in the Sun of all these different elements. And I say we already knew about them, but when the measurement was made in 1868, there were many of these lines that folks were trying to tease out and compare to references here on Earth. That's a technique we still use all the time. And there was this observation of some lines that were not yet known to correspond to anything we knew at the time. That's 1868, so that's cool. That's a big new discovery, and that's where the element's name comes from, the name helium is related to the God Helios who's God of the Sun. But it took a little while to actually identify the element, and this is something that's a story in astronomy as well. There's an element that doesn't really exist that was identified in nebulae in space called nebulium. Then it turned out it was just this really rare form of oxygen that we don't happen to see on Earth very much. And so it was sort of the same with helium, but it turned out that it's actually a real element, and it was detected on Earth less than 20 years later, looking at a spectrum of stuff from a volcanic eruption, right? So it's the kind of thing where I never thought about where would you detect helium on Earth in the 19th century? It hadn't been isolated. It's not something that you can just... There's a reason why it's not easy to get. So an Italian physicist observed it after an eruption of Mount Vesuvius and said, okay, here's the same thing that we saw in the Sun. Must be the same element. It's really cool. So it was first discovered. It's so interesting to think something was first discovered in the Sun and then we found it here on Earth. That's a rare occasion for sure.

Sarah Al-Ahmed: It was the first occasion of that, right? I mean, us being able to detect a substance off of Earth and then find it on our planet, that is really strange to think about.

Jeff Rich: Absolutely.

Sarah Al-Ahmed: And now all these years later, we use it for party balloons. I honestly wonder what scientists are going to think hundreds of years in the future when they're trying to figure out how to get helium for their instruments or their experiments, and then they learn that ancient humans used them all on party balloons. What's cool about all of this is that these are some of the observations and discoveries that people have made in the past, but this is an ongoing thing, coming up with this new eclipse. People are still doing experiments, still verifying these ideas. They're going to be studying the eclipse from space. And there's a lot of opportunities for the public to get involved. There are many citizen science projects. Are there any of these projects that you're telling people about that you would recommend?

Jeff Rich: I know that in 2017, they were asking for folks to watch the solar eclipse all along the line of sight. In 2024, the NASA has a few initiatives, they're asking for folks to capture images of the corona. So I always defer to NASA because that is the clearinghouse for both the professional scientists to find out what's going on there, but also multiple citizen science efforts in 2024. I think most of them involve trying to get a lot of data along the path of totality in a way that you wouldn't be able to do if you... We just talked about in 1919, having data from two points on the path of totality was really useful. If you have millions of people watching an eclipse across the entire path of totality, that's going to get you even more data. So the citizen science projects are a way to sort of regularize that and get people to at least snap one or two photos in the way that they can be combined with others. And I know that there's a few different science reasons. I send people to the NASA Eclipse website for all of that.

Sarah Al-Ahmed: And I'll put a link for that on this episode page if anybody wants to get involved, because I know that there are opportunities for taking images. But if you're not an astrophotographer, there are other things that people do, sometimes they study temperature fluctuations or the sounds of animals during eclipses, all kinds of cool stuff. So there's a lot of opportunities to get involved. And I think that's what I'm most excited about for this eclipse. Everybody coming together around a space event is a really special thing. And you've done so much outreach, coordination and organized so many of these events that I'm sure you have some advice. For people out there who are perhaps planning an eclipse party or something like that, what advice would you give them in the lead up to this eclipse? Because this is a moment we have to be safe as well as have a good time.

Jeff Rich: One of the things that we always address when we talk about the eclipse is proper viewing. I know that that's something that is the most important thing to stress. The easiest thing to do is get a pair of eclipse glasses to safely view the Sun. Really, you should never be looking at the Sun ever. The safest way to look at the Sun is to not look at the Sun. There are many ways to indirectly view the Sun. There are suns spotters. You can make a pinhole camera if you can't get a pair of eclipse glasses. And if you happen to be lucky enough to be in the path of totality or to travel to the path of totality, to use a resource that tells you exactly when totality is happening so that you don't miss it, number one, that's really important. We want people to see the total eclipse. We want you to safely view the eclipse, but also to know when you can safely view the eclipse. So there are a number of websites that you can use to track exactly when the total eclipse will happen where you will be. I actually really like, it's been convenient for finding out exactly where the Sun will be and when it will be an eclipse. The other thing to do is if you happen to be near an event that's in the path of totality, there are tons of public events all over North America. Then there are experts at those events who will help you know, okay, it's safe right now to view the Sun in total eclipse. And I also keep coming back to, it's really hard to describe what that total eclipse looks like. People have used lots of words to describe it, and there's beautiful photos, but you'll know it when you see it and it'll be like nothing you've ever seen before.

Sarah Al-Ahmed: I really can't impress upon people just how different it is thinking you understand a total solar eclipse and actually experiencing one, no amount of or understanding fully prepares you for what it's like. What have your eclipse has been like so far?

Jeff Rich: The first eclipse I saw was in 2017. The first thing that surprised me is actually as we got closer to totality, you did notice a change in the lighting, but it took a long time. This is another thing we tell people. I left eclipse glasses with my friends out in California and said, here's the time to go see it. Make sure you put glasses on because the Sun will never be safe to look at. But you wouldn't know an eclipse is happening because there's no change in brightness pretty much. But about five, 10 minutes before totality, it actually got cold enough where we were in Idaho that I had to run and get a sweater because it had been bright and sunny and warm, and it was all of a sudden getting chilly. I know people had said that happens, but it was weird to experience it happening in real time all of a sudden. And another thing that comes up when we talk about... for instance, here in Dallas, we're going to have some wonderful events throughout the city. We're planning those events, again, to help people know when totality happens. But another thing we sort of keep saying is we'll have MCs, we'll be talking to people through the eclipse, but when totality happens, I don't think there's much to say. We really want people to just stop and look and experience totality. And then the thing to say is, okay, now totality is over. Please stop looking at the Sun. Put your glasses back on. Look down. But it's beyond words, which makes also all that work that people are doing to get those photos, I hope they get a chance to take a moment and breathe and look at the eclipse when it happens. And the other eclipse I saw in 2019, it was the sort of thing where I thought, well, I've already seen an eclipse. I've been lucky. If I ever only saw one eclipse in my life, that's more than enough. And then I saw a second eclipse and it was close to sunset, and it was amazing. And how I would love to go see every eclipse if I could chase them all. I can see why people become eclipse chasers.

Sarah Al-Ahmed: Same. If I was a millionaire, I would go to every one of them. I keep thinking too, that I should just make a plan for the rest of my life, look up every eclipse that's going to be happening and use that as the thing that shapes my vacation destinations for the rest of my life, because it is just that awe-inspiring, it's something that I cannot describe and I cannot advocate for enough. I really hope people get a chance to see this.

Jeff Rich: And I think you touched on something which is a really great opportunity to get people excited about the universe, about space, about thinking about our place in the universe, about stopping and thinking about how things work and what we know and what we don't know, and hopefully inspire people to get excited about space and science. I hope. I don't see how you couldn't be excited about an eclipse. It's really cool.

Sarah Al-Ahmed: Well, especially in this day and age. Back in the day hundreds of years ago, I totally understand, eclipses were terrifying. Suddenly everything goes dark, the light strange in all directions. But because of this progress forward with our scientific understanding of the universe, we can now truly take a moment and not be terrified or confused in the face of these events. We can really use it as a moment to connect and understand just how beautiful our place in the universe is. And I feel like a lot of people who have no idea right now that they're going to be having that experience are right on the cusp of seeing something that might fundamentally change the way that they think about themselves and the way that we connect to the rest of the cosmos. And you could just feel it in the air, at least for me and the rest of the astronomers I know.

Jeff Rich: Absolutely. And thank you for helping to get the word out so that everybody's really excited and views the Sun safely and isn't worried about avoiding it because they're going to see something that might hurt them. We want you to see the eclipse. We want you to see it safely, but we want you to see it if you can.

Sarah Al-Ahmed: We've got all kinds of fun guides for how to view it safely, how to show it safely to your kids, all of those things. I will link all these resources on this episode page of Planetary Radio. You'll be able to find that at I'll also leave resources so that you can learn more about Mount Wilson and its history and about Carnegie Observatories because there's so much of that legacy of the way that we've discovered the universe that's tied directly to these two observatories. And I wish more people knew about that history because the more I learn, the more impressed I am with this human story of discovery, because it really is, every one of these moments is just a tale of people connecting and learning together, and it's really cool actually seeing the history in these places.

Jeff Rich: Absolutely. I love sharing the work that was done because it blows my mind every time to think about, no, these were huge discoveries made with the most amazing technology that tons of different people came together to build just so we could understand the universe. It's really, really cool.

Sarah Al-Ahmed: It's a cool time to be alive. And I hope that you, Jeff, and everybody else with you has happy weather and good viewing, and that you have one more beautiful eclipse to add to your list.

Jeff Rich: I wish you the same and safe travels, and I hope we have a lot of fun next Monday.

Sarah Al-Ahmed: Thanks so much, Jeff.

Jeff Rich: Thank you very much.

Sarah Al-Ahmed: Over the last few months of this show, we've covered a lot of topics relating to total solar eclipses. We've gone over how lucky we are on this planet to be able to observe them at all, a lot of the science behind these events and best practices for safety and observation. We've got a lot of resources on our website that you can read or share with your friends and family to enhance their eclipse experience, including our newest article, Experiencing the Total Solar Eclipse Without Sight. You can find all of these resources and more on our website at That also includes an interactive eclipse map that'll help you find the best places for observing this. If you don't live near this total solar eclipse, there's going to be more opportunities for you to observe one in the future. Of course, everyone is welcome to watch our live stream of the total solar eclipse, but there are also three more of these events on Earth that are going to happen by the end of the decade. There's going to be one in 2026 go over Greenland, Iceland, and Spain. Then there's a big one in 2027 that'll pass over numerous countries. That includes Spain, Morocco, Algeria, Tunisia, Libya, Saudi, Arabia, Yemen, and Somalia. Then if you've missed those two, your last opportunity for seeing a total Solar eclipse before the end of the 2020s will be in 2028. That's going to pass over Australia and New Zealand. Now, let's hear from Dr. Bruce Betts, our chief scientist here at The Planetary Society for What's Up?. This is going to be my last moment to talk to him before we're high-fiving in Texas for our Eclipse-O-Rama event. Hi, Bruce.

Bruce Betts: Hi, Sarah.

Sarah Al-Ahmed: I'm so excited to actually get on my plane and fly out to Eclipse-O-Rama. I really hope we have clear skies when we get there.

Bruce Betts: Yeah, me too. Not the thunderstorms they're predicting, which should be very exciting.

Sarah Al-Ahmed: That'll be exciting either way. I think about this, as I get closer to eclipses, it's always like, what am I going to feel if I end up getting rained out or clouded out? And this time, I feel like it's going to be fine either way, even though I'd be bummed out not to see the total solar eclipse, because we're going to have hundreds of Planetary Society members together at Eclipse-O-Rama. So either way, I think it's going to be a great time.

Bruce Betts: Yeah, it'll be good. And even if it's cloudy, as long as it's not like massive thunderstorm cloudy, we'll see some effect, and hopefully we'll see it.

Sarah Al-Ahmed: So this week we got to talk about some of the discoveries that have been made during total solar eclipses. And I did learn some that I hadn't heard of before. But the big one that I learned about in school growing up was about in 1919 when they used the total solar eclipse to validate Einstein's theory of general relativity, which is such a cool thing that we actually managed to prove that at that day and age. But since that point in time, we've learned so much more about the way that relativity impacts our universe. Since then, what are some cool space things that we've been able to observe that are caused by this warping of space-time due to gravity?

Bruce Betts: All sorts of things. Personally, I just believe, because every time they test Einstein's theories, he's always fricking right. It's really annoying. And indeed, they have... so they have the solar eclipse with having the bending of light around a star. And then now we see gravitational lensing all over with our big fancy telescopes where you're seeing the galaxy's size, even objects acting as lenses that take light coming from behind it, and they bend around, which is what they predicted. General relativity says gravity will bend light, which bends my brain. But it's true. And we also have done some crazed experiments, notably, one I'll mention is Gravity Probe B, which was a multi-decades development of a really impressive and unbelievably precise experiment flying a satellite and measuring gyroscopes on board and how they changed. And that verified to a pretty good accuracy, the general relativity predictions of frame dragging. So the whole weird as the Earth spins, it drags space-time with it.

Sarah Al-Ahmed: Wow.

Bruce Betts: It's still pretty cool.

Sarah Al-Ahmed: I was also really, really impressed with that Event Horizon Telescope and all of the efforts that it took to try to not get a direct image, but at least get enough information about black holes that we could create these simulated images of them.

Bruce Betts: Black holes are another whole weird, weird thing that you'd think shouldn't exist, that silly Einstein's theories, you work through them and they exist, and weirdly, they do. You also have just a lot of, for me, is a human brain, a lot of weird stuff that happens due to general and also special relativity. GPS has to adjust for general and special relativistic effects on a regular basis because the dominant effect is that gravity slows down time. And so the spacecraft [inaudible 00:51:49], gravity isn't that much different, but at their altitude it is less. And so those clocks move at a different time, but they're moving, so there's special relativity effects. And so there are actually non-trivial adjustments, even from day to day, even though it's some number of microseconds per day that they make an adjustment, but it has kilometers results in terms of some of the weirdness. So anyway, it actually strangely affects our weird, modern technological lives, not our normal sitting around lives. And then there's the whole weirdness of... Sorry, I treat all of this, it's like magic that's actually true, of the astronauts. Clocks are moving at a different rate than the people on the surface and so technically they're living a little different amount of time. And I don't know whether I've ever mentioned on the show, but the honest answer is this is why I became a planetary scientist, because studying these things in school hurt a lot, and so planets, I get it. And then I was really a wimp and studied surfaces of planets I could actually imagine standing on because liquid... Anyway, I ramble, but this stuff is amazing, fascinating and ow.

Sarah Al-Ahmed: It's some intense stuff. I mean, I think about the fact that our ancestors didn't need to this knowledge at all, and yet without this knowledge, seriously, if I tried to use my GPS just to get to the local store or something, I would be kilometers off track if we hadn't taken these time dilation effects into account.

Bruce Betts: Which is what everyone was before GPS involved, just you'd go to the store and you'd end up kilometers away. I remember those times. Now that may have just been me because I get lost really easily in urban environments.

Sarah Al-Ahmed: School stuff though. I mean the moment I really had to internalize the fact that down is always the direction of slower time, it's a trip

Bruce Betts: That explains the indigestion I've never worked out. I'll internalize that now in a proper way and hopefully do better.

Sarah Al-Ahmed: Well, all right, what is our random space fact this week?

Bruce Betts: I can't compete with that downtime thing you just did, but maybe I can in the practical world of applied stuff. So let us do, well, we'll do different times. So Gravity Probe B, in order to measure this effect with their gyroscopes that they had, the two effects there to measure, they produced the most nearly spherical objects that have ever been produced. The spheres of the gyroscope, which were, I forgot, but a few centimeters in size, they were accurate spheres to within 40 atoms.

Sarah Al-Ahmed: How did they do that?

Bruce Betts: Batch. Sore. Sore.

Sarah Al-Ahmed: I'm definitely looking up videos on that.

Bruce Betts: Yeah, no. Hey, I just quote the facts, but it's darn impressive. Part of, it was, I think Stanford and Lockheed activity. Yeah, pretty impressive. Now, technically, another one of the couple of their gyroscope spheres have been eclipsed by a new crazed, weird physics experiment spheres, but apparently a couple of them still the roundest... well, not roundest, but most nearly spherical objects that humans have ever created. I plan on creating something more at Eclipse-O-Rama. I am announcing now I will take modeling clay and make the roundest sphere ever in the history of the universe.

Sarah Al-Ahmed: I am looking forward to seeing you trying that. I'm trying to imagine how you would even begin to attempt it. And then how would we test its thickness, Bruce? We're going to have to build a science lab.

Bruce Betts: Darn. We can't. You'll have to trust me.

Sarah Al-Ahmed: Never.

Bruce Betts: Well, on that not. All right everybody, go out there, look up in the nice sky and think about the most nearly spherical object you've ever seen. And optionally, whether you trust me. Thank you. Good night.

Sarah Al-Ahmed: All right everyone. We've reached the end of this week's episode of Planetary Radio, but we'll be back next week to share the amazing story of Venus's quasi-moon Zoozve with one of the hosts of Radiolab, Latif Nasser. If you love our show, you can get Planetary radio t-shirts at, along with lots of other cool spacey merchandise, including safe eclipse glasses. Help others discover the passion, beauty, and joy of space science and exploration by leaving your review and a rating on platforms like Apple Podcasts and Spotify. Your feedback brightens our day and helps other curious minds find their place in space through Planetary Radio. You can also send us your space thoughts, questions, and poetry at our email at [email protected]. Or if you're a Planetary Society member, you can leave a comment in the Planetary Radio space and our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our members around the world who love to wonder at our place in space. You can join us to help us share that joy with everyone else at Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. We wish you all happy, observing and good weather, and until next week, ad astra.