Storms on the Sun
This month on Naked Astronomy, we're setting our sights on the Sun. How do storms form on the Sun? How can they wreak havoc here on Earth? And what can we do to predict them? To find out, Ben McAllister and Adam Murphy are joined by University College London solar physicist Stephanie Yardley...
Ben - Unsurprisingly, given it's almost always the brightest thing in the sky. People have been looking at the Sun for as long as there have been people, and they've been observing it in a scientific-adjacent fashion for a very, very long time.
Adam - Yeah. A really long time. People from various cultures have worshiped the Sun, or they've seen it as a representation of the divine at different times throughout humanity's history.
Ben - Before there were telescopes, ancient astronomers, pre-telescope astronomers had even spent enough time studying the Sun to know about the existence of what they call what we now call sunspots, which are dark patches on the surface of the Sun that were visible with the naked eye through careful observation.
Adam - And that careful observation was often done. The ancient Babylonians of hanging gardens fame, they were aware of solar eclipses, when the Sun is obscured by the Moon's shadow. And there's some evidence that they may have even predicted them using the numerical rules they had available to them
Ben - For a long time, people believed that the Sun orbited the Earth. It was just another thing up there, like the Moon. This theory where the Earth was the centre of the universe, and everything kind of revolved around it. But of course, we now know that that's not true. There's nothing particularly special about the place of the Sun in the universe, the Earth orbits the Sun and the Sun orbits the centre of the galaxy. But that was at one point a controversial viewpoint. An astronomer named Giordano Bruno was actually executed, burnt at the stake for publicly stating his belief that the Earth was not the centre of the universe, that the Sun was well, if not the centre of the universe, at least at the centre of the Earth's orbit.
Adam - And at least now we don't burn people at the stake for that kind of thing. And with the advent of the telescope and modern astronomy, we began to understand the Sun a lot better. And what we learned is that there isn't actually all that much special about it. It's the same as all the other twinkling lights in the sky. And even then, it's not that much bigger. It's sort of middling in size, middling in temperature, kind of a bog standard star. It's just, it's the one that's closest to us.
Ben - Hard facts and figures about the Sun, some stats for you. First thing we need to know, it's about 4.6 billion years old. It's a similar age to the Earth indicating that the solar system formed at a pretty similar time in the universe's history.
Adam - And if we want to talk more facts and figures, it has a diameter, so from one side across to the other, of 1.4 million kilometres. And just because that number is ridiculous and you want to get an idea of scale, the Earth's diameter is only 12,000 kilometres. So it is that much bigger than we are.
Ben - The mass of the Sun is a number 2, with 30 zeros after it, in kilograms, which again, to give you some kind of context there, is about a million times as massive as the Earth is, which is just absurd. And it is 150 million kilometres away. So you could fit about a hundred of the diameter of the Sun between the Sun and the Earth. So it's, you know, pretty far.
Adam - It is also pretty hot. The surface temperature of the Sun can get to 5,500 degrees Celsius.
Ben - It's, you know, nearly that hot down here in Australia sometimes.
Adam - Yeah, nearly that hot, but as well as that, it's also got strong magnetic fields around it. The fields at the surface can reach about 0.4 Tesla, which doesn't sound like much, but it's about the same as a junkyard car magnet, which can toss cards around. And when you think that the average magnet just goes on your fridge, it is a big magnetic field.
Ben - So, we've heard about 4.6 billion years old, but where did it come from? How did it form? What does it do all day? Well, the Sun formed when a bunch of gas from somewhere else in the universe started to clump together due to gravity, you had this pocket of over-dense gas that started pulling inwards, and pulling inwards. And as it came closer and closer together, it had to lose gravitational potential energy, like a ball falling from the upper atmosphere in the Earth, falling down towards the Earth. It's losing potential energy and it's becoming another kind of energy in the case of the ball falling towards the Earth. It's becoming kinetic energy. The gravitational potential energy that the gas is losing is being radiated away. And the gas is getting hotter and hotter and hotter and denser and denser
Adam - And hotter and hotter and denser and denser until eventually the pressure and the temperature becomes so high that something amazing happens. And that is nuclear fusion.
Ben - So what is nuclear fusion? It's kind of a buzzword. We can describe it like this: in the early universe, after the big bang, or a short time after the big bang comparatively to the age of the universe, the only stuff that there really was, was hydrogen and a bit of helium and a very small amount of heavier elements. Hydrogen is a very, very simple element. It's a single proton, if it's in its atomic form, it's with a single electron around it, or if it's an ion, it's just a single proton. So very, very small. And if you get it dense enough and a high enough pressure and high enough temperature, a bunch of hydrogen, those hydrogen particles, those single protons will actually fuse together to create bigger elements like helium and other things in those very, very, very high density, high pressure, high temperature conditions.
Adam - The key thing there is that when these two hydrogens are fused together to create helium and all that other stuff under this high temperature and pressure, the mass of the resultant helium is just a teeny, teeny very tiny bit less than the mass of the initial stuff that went into it. But how does that change in mass mean that you get energy out the other end?
Ben - Well, you've probably heard of Einstein's famous E=mc squared equation, which teaches us that mass is really just another form of energy. So when that little bit of mass goes missing as the hydrogen together to create helium, it hasn't actually gone missing at all. It's just converted into a different form of energy and it's sprayed out in the form of light, sunlight.
Adam - Exactly. And all of that light, all that sunlight is just missing mass from the elements fusing together and getting beamed away from the sun.
So what impact does the Sun have on Earth? It might seem like a bit of a silly question, but a simple answer: provides all of the light and heat for one, you know, we wouldn't have any light to see on Earth or a very, very small amount from distant stars if it wasn't for the Sun. And it would be very, very cold. We'd be rocketing through the void of space, just like all of the comets and stuff that fly out there that aren't bound to a star.
Adam - Of course, sometimes too much light gets in and all that light gets trapped in the atmosphere of the planet. And you end up with a greenhouse effect, that's contributing heavily to global warming, but we're not going to dwell too much on those negative things. This is a show just about the Sun itself.
Ben - Another awesome thing that the Sun does for us is provide energy to plants, which can then take that energy and undergo photosynthesis, where plants consume photons of light from the Sun and create sugars, that we and other animals can consume for energy, that are basically eating sunlight and turning it into other stuff. It's quite incredible.
Adam - I love that, eating sunlight, but there's one other effect as well that it does. And because of its gravity, it keeps us orbiting around and it keeps us orbiting the centre of the galaxy around the Sun, which is nice because otherwise we'd just be a cold ball of ice going through the empty void of space all alone.
Ben - But the Sun isn't just a glowing ball of plasma, which gives us light heat and energy and keeps us in our place in the universe. It can also exhibit a lot of scarier, more explosive and potentially dangerous phenomena.
Adam - Very dangerous. You may have heard of solar storms. Well, they are real and they can wreak real havoc here on Earth.
Ben - We spoke to a solar meteorologist Stephanie Yardley to hear all about these storms and what we can do to predict them
Adam - But, to get started with, she told us more about the Sun itself.
Stephanie - Well, it wouldn't be a very nice environment. Like what you've just said, we wouldn't be able to survive it. We've designed some spacecraft recently that are going very close to the sun. So within the orbit of Mercury Solar Orbiter, for example, and they've had to be designed with heat shields and various materials. And it's been really difficult to design these kinds of instruments just because of how hot and unfriendly the Sun is. I think that sums it up: hot and unfriendly.
Ben - Yeah. Right. I mean, how hot are we talking?
Stephanie - So we're talking millions of degrees, right? So the Sun's surface is thousands of degrees, but it actually gets hotter as you move away from the surface. So we're talking about 10 million degrees, something you would not want to be close to at all. Absolutely not.
Adam - How does that work? That seems counter-intuitive that it's hotter as you go further away from it. How does that work?
Stephanie - Yeah it's one of the long, outstanding problems of solar physics. It's been around for decades and we're not entirely sure. It's one of the big problems. It shouldn't work that way. Like when you move away from a radiator, for example, well you get cooler, but if you move from the Sun surface outwards, then it actually gets hotter. So there must be some sort of heating mechanism that's at work here and we've narrowed it down to the two camps, essentially that argue against each other in the community. So you have things like the magnetic field is responsible. So the magnetic field of the Sun is responsible for so much, like solar storms and space weather, but it also could be responsible for heating the sun. So breaking and joining of the magnetic field and releasing energy could essentially heat the sun's atmosphere. But then you also have waves. So the propagation of waves through the atmosphere as well could produce heating. This is something that we still work on today and is very much a hot topic.
Adam - Do you have a camp or are you keen to just watch the scientific gang war from the sidelines?
Stephanie - Yeah. I just watch from the sidelines. I mean, it could be a combination of both, which is probably most likely. We don't know, the science doesn't add up at the moment, the numbers don't add up. So we need to go back and continue working on this.
Ben - And it's not just the high temperature, as you were saying. There's also a very, very high magnetic field, which could also be pretty unpleasant, I suppose. And certainly damaging for spacecraft.
Stephanie - The Sun is very active well, depending upon where it is in its cycle. So the Sun has an 11 year solar cycle and it's all dependent upon these magnetic fields. And when we're near a maximum of the cycle, we get a lot of activity due to these really strong magnetic fields, such as coronal mass ejections. So these are eruptions that come from the sun, we get highly charged particles. We get just the expansion of the Sun itself, which is known as the solar wind. This is constantly hitting us. If we didn't have our own shield, the Earth's magnetic field. We would be in trouble. So it is a very hostile star.
Ben - Hostile. It's a nice way to describe it. So you've hit on a few things there that might partially answer this question, but yeah, I guess, can you tell us just generally, what does the Sun do all day and all night while we're not looking at it?
Stephanie - I haven't looked today, but it's probably quite quiet because we're at a low in the solar cycle. So we're near the minimum. So we go through minimums and maximums and it's either, I guess, quiet or stormy conditions, you'd call it. We have sunspots on the surface, and this is where a lot of the activity comes from. This is a region of really strong, concentrated magnetic fields. And they appear dark on the surface. So you can look at them through telescopes or using glasses so you can look at the sun. These can produce eruptions or these highly energetic particles that cause all sorts of effects on Earth. But currently I think it's pretty, unfortunately for us, it's pretty quiet at the moment because we are during this lull.
Adam - And what could we expect to happen, what would be different if it was at the peak of that activity?
Stephanie - So you do get a lot more eruptions. So the statistics say it's probably about 0.5 day right now, but then say in solar maximum, we have maybe six per day. It just depends. So because we have more of these regions on the surface with these strong magnetic fields, you get a lot of breaking and releasing of the energy. You just get generally a lot more of these eruptions and any kind of eruptive phenomenon from the sun. So these are the kind of busy times, I guess, but that doesn't mean we don't get events occurring right now. I think there was one either yesterday or the last couple of days that will potentially be headed towards Earth.
Ben - You've mentioned there a couple of different things. You mentioned solar storms a few times. You mentioned sunspots a moment ago. I want to jump into solar storms in a minute, but I've heard these terms. You hear things like solar flare, sunspot, solar storm, are those all the same thing? Are they different things? What's the difference there?
Stephanie - We have so many names for so many different things. As physicists we like to categorise things. We get caught up in this terminology. So sunspots are these dark patches that you see on the surface of the sun. And this is just an indicator that you've got some really strong magnetic fields there. And this is where most of the activity comes from such as solar eruptions for example. Solar storms is just kind of a broad term, which incorporates more these kinds of eruptive phenomena that come from the sun. So there's generally three different types. We have the solar flares, which are really intense, bright lights from the sun, which you see, and this is because of the magnetic field changing and releasing a lot of energy. And these occur very quickly. So you see these brightenings probably up to an hour or a couple of hours, but they onset very quickly. The eruptions, or we call them the technical term, coronal mass ejections. These are these huge bubbles of magnetic field and particles that essentially race towards us at thousands kilometres per second, and can hit us here at Earth. And then you have these solar energetic particles. These are high energy particles that come from the Sun and they can reach us even quicker. So eruptions actually take maybe even three to five days. I think the quickest one was 17 hours to reach the Earth, whereas energetic particles take minutes, maybe 10, 20 minutes to reach us. So we've got all these different types of solar hazards, essentially, that can affect us here. And that's not even talking about the constant stream that we get from the sun. This is the solar wind. So the Sun doesn't just stop in space. We have this expansion of the Sun and that those particles hitting us and hitting us now also can cause things like the aurora and damage to our satellites as well.
Ben - All right. So let me see if I've understood this. So there's always a solar wind, particles coming from the sun. Then you've got this bucket term, solar storms, which contains things like coronal, mass ejections, and solar flares and streams of high energy particles. And so that's kind of like, those are all different kinds of solar storm. And then a sunspot is just like a region on the Sun where those kinds of events are more likely to occur.
Stephanie - Wow. Perfect. Great. I can just leave now, right?
Ben - Yeah. Wow. Well, there you go. Thank you very much. This has been our show. Thanks for coming on. Yeah. Okay, great. Thanks for clearing that up.
Adam - One of the things I love is if you talk to a botanist, the Sun is this gentle, wonderful life giver that feeds all our plants. And then when you talk to an astrophysicist it's a damaging fireball in the sky! Be afraid!
Stephanie - Yeah, and if you go to the other end and you talk to astronomers or astrophysicists, they'll be like, Oh, the sun's really boring. It's magnetic field’s really weak. And we don't really care about it.
Ben - Yeah. It's not like a magnetar or something. So what do we care?
Stephanie - Whereas I'm like, well, you study stars right out in the universe that, you know, what kind of effect do they have on us on a day to day basis, where our Sun is our closest star. It's the one that we can study in the most detail. So we can send these satellites up there. We can have these ground-based telescopes and look at the surface in beautiful detail, particularly with some of the new telescopes that we've got recently. And it affects us on a daily basis. It sends us these lovely solar storms that we thankfully are protected by our Earth's magnetic field. Although it still obviously causes problems here on the ground. And that's another reason why we want to try and predict these events.
Ben - Yeah. Can you say a bit more about that? You know, you're jumping right into it. Why are we interested in studying these solar storms and energetic solar events at all?
Stephanie - Most people will be aware of the Aurora. And these are kind of like the nice consequences, I guess, the pretty consequences of these solar storms. So when they're headed towards Earth and they interact with the Earth's atmosphere, then you get the lovely aurora. And if you're lucky enough to see these, it's a great experience, but also it can damage satellites and also any form of electronics. It can affect the national grid, anything that relies on power essentially. And so we really want to try and predict these events so we can act, so we can try and protect some of our infrastructure, but this is really difficult to do because like weather prediction, well, I think space weather prediction is probably further behind than weather prediction at the moment. Most of our efforts are focused on, we see an eruption coming from the Sun and then we model it and how it propagates towards us and then hope that our model is right. And yeah, a lot of the time we don't get it right, because there has to be certain conditions of this eruption. They don't always affect us. Sometimes they just pass over us. And this is all dependent on the magnetic field. We can probably predict their arrival time within about 12 hours. But someone, say from the national grid will want three to five days warning. We're quite far away from being able to provide this at the moment. And that's just the national grid. There are people that use radio communications or global positioning systems and stuff like that. It really affects our communications. We're in trouble when one of these events happens and we rely on something, say in a natural disaster, and we're relying on radio communications, for example, and they just stop and they cut out. Then it is a problem and it will cost millions of pounds. You get power outages. For example, there was an event in 1989 in Quebec, in Canada, and the whole of Quebec lost power for about nine hours. And this cost millions of pounds. And you can cause permanent damage as well to the transformers, which take months, years to fix.
Adam -What's actually going on? What connects the Sun having a moment to messing up the national grid?
Stephanie - I like how you describe the Sun, the Sun having a tantrum. The Sun having a moment. For example, if I take the eruptions, it's these huge bubbles of plasma and magnetic field that race towards us, and they hit the Earth. Well, they hit the Earth's magnetic field and it interacts with the Earth's magnetic field. So then you're essentially getting high energy particles in the Earth's atmosphere, which is one effect. And that obviously causes the aurora as well. And then also what happens because of these electric currents, you basically affect the magnetic field at the surface as well. And these induce currents. So you are essentially inducing currents, which then obviously play havoc with the national grid, for example, or anything that relies on power, essentially. So one of the biggest events that you'll hear thrown around a lot, say the Carrington event in 1859, technology wasn't what it is today. For example, they had the telegraph operators getting shocks from their telegraphs and they were operating by themselves. Yeah. Just because of these currents that were being induced.
Ben - That powerful?
Stephanie - Yeah. That's kind of our, we use it as our worst case scenario. That was a particularly strong event, the eruption actually arrived in 17 hours. So it was really, really fast.
Ben - Would it be fair to say that it's kind of like an electromagnetic pulse, that a sci-fi and/or real thing that people talk about, as a way to sort of disable communication systems?
Stephanie - Yeah. I guess you can essentially call it that. It's annoying that we can't say for certain when this is going to occur , we watch the Sun and we see an event occur and then we're thinking, okay, well we'll model this and see what happens. And a lot of the time we get false alarms because of it. And this is also a problem, right? So if we issue an alert and, for example, with the energetic particles, we are worried about radiation. So when you are flying in an aeroplane, no matter whether it's just a commercial flight or particularly space flight, when you're higher up, then you're worried about the radiation doses you will receive. So having an alert sent out saying, we think there's going to be a radiation storm because there's an event that's occurred at the Sun and then it's not happening. Everyone obviously reacts to that. So for example, airlines might fly at a lower altitude or avoid polar routes so that you don't get an increased dose of radiation, but then that costs money because it costs them in terms of fuel to fly at a lower altitude, but then that was waste then. So if we keep sending out false alerts, then the aviation industry is not going to be very happy with us.
Adam - So then going back to like the prediction thing, what are we actually doing at the moment in terms of getting to the point where we can predict them? What's the current research look like?
Stephanie - So at the moment, as I've said, we sit and stare at the sun. We sit and watch the sun. We have satellites up there that look at say, the eruptions that are coming and then we can model them. And so one of the things is to improve our understanding of these regions. And that's what I'm interested in. So looking at the sunspot regions and figuring out what kind of regions produce these eruptions or energetic particles. So what kind of properties that we can then feed into these models and then improve the prediction. Because a lot of these models are based on the observations that we have. If you can figure out what parameters or what properties of these regions that are most important for these events, then you can better inform the models. And then obviously you can also work on the models and improve the models themselves because computing time is expensive. And obviously we're doing this in real time. We're trying to forecast as quickly as we possibly can. And so the models won't have all the physics in them. We can't do that. They would take months or years to run. We wouldn't be able to run them. There are two paths, really. You have the actual science, like what I'm doing, looking at these regions and trying to figure out, you know, why these particular regions are productive. Or you have the space weather side, which is actually looking at the models, and the end users and looking at what they want out of these models. Like what information and what warnings they want. So there's two streams, really. The research side, and then the space weather prediction side. And they do link together as well.
Ben - Would it be fair to say that your research on the prediction side is then centered around looking at the sunspots, the regions where these things happen and try and figure out, like, is it kinda like data science-y to some extent, like looking at past data and saying like, Oh, ones that have been this shaped and this size or whatever had these kinds of events and then using that to predict future events?
Stephanie - Yeah. That's precisely it. So we can look at the magnetic field imprints of the sunspots essentially. So we're looking at the magnetic field on the surface. And I look at this data and say, what are the sizes of those regions? How complex are they? You know, what kind of structures we see. You look at various properties of these sunspots over various days, leading up to eruptions, and then try and see what was different about these regions compared to regions that don't produce these eruptions. And this is what a lot of the community's looking at at the moment, what properties we can get from the data to then inform these models and to inform these predictions. One of the problems that we have is this is only looking at the magnetic field on the surface. What we'd ideally like to do is look at the magnetic field throughout the atmosphere. And these measurements are really difficult to make. And so we don't have these routine measurements. And we think that actually, maybe if you had the surface magnetic field, along with what's going on throughout the atmosphere, this might actually help us. And this is what one of the new telescopes has recently been built, actually looks at the magnetic field in the corona. And this is where models come in as well. We can also use models to model the outer atmosphere's magnetic field. But again, these aren't going to be exactly spot on. They give us a general idea and also you then struggle with computing time. Again, these models aren't necessarily very fast. So yeah, it's trying to figure out what information is needed. And with the, like you're saying about data science, we can use all these methods that are coming up elsewhere. So a hot topic right now is things like machine learning and artificial intelligence, and going back through all the data sets and trying to do a statistical survey of what regions were producing these eruptions and these kinds of phenomena, and which regions weren't, in training their models on the data sets.
Adam - Just wondering, would it be kind of an analogy to normal weather, would it be fair to say that kind of where it is at the moment? It would be like if we saw a storm on the planet and then after it happened, we'd be able to say, well our model predicted it. That's what that storm would have done. So we're right. And maybe we'll be able to predict it in the future.
Stephanie - Yeah. That sounds about right. And there are so many different communities across the world using different models and producing different predictions. We have it with the solar cycle as well, looking at how, this is a big one as well, how strong the next solar cycle is going to be. So you have a prediction panel that comes together and they predict how active the sun's going to be. So the solar cycle is measured by looking at the number of sunspots over the 11 year cycle. And so you have these various predictions that people argue about, no, we're going to have a very quiet cycle. Actually, it's going to be very active. And they, again, because they're based upon models and we don't know everything about the sun, then obviously they can be right or wrong. So there's a lot of arguments about what the sun's going to do in the future.
Adam - And do you think we'll ever reach the point where, you know, we'll be able to say on the weather forecast, you know, cloudy with a chance of solar flares?
Stephanie - Like I said, the kind of forecast we have is like there's a 50% chance. There'll be the solar flare today, like this level of activity. So we already have that kind of prediction. It's just the, whether we get it right or not is another matter.