In Our Time - The Sun

Episode Date: July 10, 2014

Melvyn Bragg and his guests discuss the Sun. The object that gives the Earth its light and heat is a massive ball of gas and plasma 93 million miles away. Thanks to the nuclear fusion reactions taking place at its core, the Sun has been shining for four and a half billion years. Its structure, and the processes that keep it burning, have fascinated astronomers for centuries. After the invention of the telescope it became apparent that the Sun is not a placid, steadily shining body but is subject to periodic changes in its appearance and eruptions of dramatic violence, some of which can affect us here on Earth. Recent space missions have revealed fascinating new insights into our nearest star.With:Carolin Crawford Gresham Professor of Astronomy and Fellow of Emmanuel College, CambridgeYvonne Elsworth Poynting Professor of Physics at the University of BirminghamLouise Harra Professor of Solar Physics at UCL Mullard Space Science LaboratoryProducer: Thomas Morris.

This BBC podcast is supported by ads outside the UK. Thank you for downloading this episode of In Our Time. For more details about In Our Time, and for our terms of use, please go to BBC.co.com. UK slash Radio 4. I hope you enjoy the programme. Hello, 26,000 light years from the centre of our galaxy, in one of the outer reaches of the Milky Way, is an unremarkable little star. Astronomers describe it as a G-type main sequence star,

and in most respects there's nothing interesting or a new star. usual about it, but ever since humanity first walked on the planet, it's been an object of fascination. For one very good reason, it's the sun, our sun. The sun's been burning for four and a half billion years, and it's the source of all our energy. At its core, nuclear reactions of almost unimaginable power generate heat and light, which takes 100,000 years to penetrate the surface, but then only another eight minutes to reach us on Earth. The greatest minds have been studying our nearest star for millennia, but only in recent decades have we begun to to have some inkling and the astonishing processes at work inside it.

With me to discuss the signs of the sun are Carolyn Crawford, Gresham Professor of Astronomy and Fellow of Emanuel College, Cambridge. Yvonne Ellsworth, Pointing Professor of Physics at the University of Birmingham, and Louise Harrah, Professor of Solar Physics at the UCL Mallard Space Science Laboratory. Caroline Crawford, let's start with the basics. What would you give us a quick idea of the size, nature, sun? Well, as you say, it's a star, our nearest star, which we view from the relatively close vantage point of 150 million kilometres away. So this is astronomically speaking, of course.

And it's huge. It's got a diameter of 1.4 million kilometres, which translates about 110 times the width of the Earth. And its volume is so large you could fit over a million planet Earths within it. So this is why it dominates our solar system. it's incredibly massive. If you added up all the planets, dwarf planets, moons, comets, asteroids within our solar system,

it's still 700 times more massive than all the rest of the solar system put together. So its gravity dominates, it sits at the centre of the solar system and pulls everything else in orbit around it. Other things to say, well, if you work out from that mass and that volume, you find that its average density is quite low,

so it's less than a quarter of the density of the earth. So it's not made from the same material. It's mostly gaseous. And it's incredibly hot. Temperatures ranging from over 15 million degrees at the core up to just short of 6,000 degrees on the surface. And so it is, you know, incredible privilege to be able to see a star at such close quarters.

Can you tell us about how it came into existence? How and when? Well, this is conjecture from what we know about the laws of physics. but also from observing other stars that are forming within our own galaxy, within the spiral arms. And we reckon it came into being about four and a half billion, so it's four and a half thousand million years ago. And all stars formed from the material that lies in what we call the interstellar medium.

So this is the space between the stars. It's not truly a vacuum. There is material in there. And most of this interstellar medium is transparent to our eyes. It's either very cold or very hot. and in regions where you maybe get colder, denser pockets of gas of the interstellar medium, it starts to collapse under gravity. Now this is grossly simplifying, but of course the interstellar medium is not uniform.

There are areas which are colder, denser than the others. And if you get regions that are just slightly more massive, then, you know, slightly denser, they've got slightly more mass. They're going to have more gravity. They're going to pull in more material close to them. They'll get more massive, more gravity. They'll pull in more material. And you get a process of runaway gravitation.

collapse. So to be even grosser than you, which is easy for me to do because I know about one million times what you do. It's a lot of dust coming together and it achieves a sort of mass which begins to follow laws of gravity. That's right. And it's not just gas, it's also dust. I mean, there's stuff in the interstellar

medium, some of it's primordial, some of it is material that has been processed through stars. But you're right, it begins to collapse down and it forms a sort of cocoon. And the thing about, you know, by conservation of energy, if material falls under gravity, it heats up. So right at the densest core of this cloud, the material's going to heat up, it's going to get more compressed, and eventually it'll reach temperatures of, you know, sort of 18, 16 million degrees.

And at that point, it becomes a proto star because it's hot enough and it's dense enough for that process of nuclear fusion to begin. And at that point, you've got the young star just starting. Louise Harrah, would you tell us something of the composition of the sun and what it consists of? Sorry about that. Triple question. And how we know what you've got to know what you're going to tell us? As Karen had said, the sun is basically, it's just a big ball of gas. And we measure it. It's made mostly of hydrogen.

So it's roughly 90% hydrogen. It's maybe 8% helium. And the rest of it's made up of things like iron, carbon, oxygen, nickel, just very small amounts of that are up here and that. We can measure it in a different way. the way we know what's in the sun is we can use spectroscopy and that's basically

dispersing light in different ways so you can measure different energies in the light. Can you just be more specific about that? It's as if you're looking... When you've got a rainbow, a rainbow is created by dispersing the light through raindrops. So what you're

doing when you're trying to observe the sun and measure its composition is you're doing exactly the same thing and you're able to pick up the chemical elements. It's like a fingerprint on the sun, so you can pick up those different elements there. So helium, for example, was first discovered on the sun, and that's why it's called helium,

because it was named Helios after the Greek sun god. So it was discovered on the sun before we discovered it in the earth. So we can tell a lot from spectroscopy, and that's how we know what the abundance is of different elements. So we've got hydrogen, helium, and about 8% of other bits? 1% of other bits. It's mostly 99% hydrogen helium.

And what does the 1% of other bits bring to the table? It makes it easy for us to probe the sun. Because that's what you call metal, but we wouldn't call it. Yeah, it's very highly ionising, so it's acting as a gas, basically. So although you've got these what we view off as metals, they're so hot and the density is so low that they behave quite differently. And we'll come back to the latest research later, but just to get a taste of it, are we getting a new instrument, us on microscope,

getting us near and near to know more and more about it? Are we finding out a lot in a short time? Yes, we've got a lot of spacecraft that are observing the sun. We've got telescopes on Earth that are observing it. And those allow us to look at it in really, really fine detail. And as Carolyn said, it's our nearest star. It's our star that gives us heat and light. And we've got the privilege to be able to observe in detail.

We can't do that in any other star. So it allows us to see physical processes in the way we can't do any other way. Do you think it's like other stars? So by studying the sun, you think, oh, this is what stars are like? Is there such a thing as a typical star? And if so, is the sun a typical star? The sun is, well, it's actually quite a boring star, really. You keep using you're boring.

It's in your head, and I thought, well, you know, damn it, it's not boring for us, is it really? definitely not boring for us. And there's a lot of activity in the sun. You get a lot of dramatic explosions on the sun that seem big for us. Yeah, but is it like other stars? It's an average star, so it's kind of halfway through its lifetime.

There's a lot of stars. It lies on what's known as the main sequence that you described in the introduction. And that's where 90% of the stars lie on that main sequence. And that's where stars behave when they are conferring

hydrogen and helium. If the gravity isn't big enough to heat it up enough so that it can't produce fusion, can't get that energy, then they haven't started creating the energy yet. So the sun's in the main sequence phase. It's about

four and a half billion years and you think it's got about 5.5 billion years to run. So what, can you say again what you mean by main sequence? It simply means that that is the lifetime of the

lifetime of the star in which is creating helium from hydrogen so it's using that fusion process to produce all the energy that we eventually see as light coming from the sun. Thank you. Yvonne Ellsworth we're getting into detail

but I'd like to have more about the structure of the sun can you if we look say we could I know it's all gas right and it wobbles all the time so you could slice it into like an apple what would you see? Okay it's an interesting concept taking a knife to the I'm considering it's so hot and you'd melt it, but let's put that to one side. Okay, in the centre you have a core, and the core, as we've already described,

is where the nuclear processes happen that create the energy. How big is the core? 10, 20% of the radius of the sun. I tend to think in terms of what fraction of a radius it is, rather than remembering all these terribly big numbers. I think, well, okay, it's about 10, 20%, and so on. So that's the core. And then you get into a zone which is quiet.

It's very hot. Gases are moving around a lot. You didn't tell me enough about the core, though. What's really going on in the core? Okay, you have lots of hydrogen and a rather smaller amount of helium, and those are the things that absolutely dominate there, even though the metals are still around. So the temperature is such and the pressure is such,

density as such that you can turn hydrogen into helium and in so doing release a small amount of energy so the famous Einstein's law allows you to say how much energy comes out for a certain loss of mass so I don't know 1% of the mass gets lost in the process and comes out as energy the key thing to note though is that unlike a bomb that goes off in a very

well explosive is probably obvious but very quickly, some of these reactions actually are not very likely. So the whole thing happens in a very slow and controlled way, thereby allowing the sun to have this enormous lifetime, sort of 10 billion years or whatever. So what's slow in terms of the sun? Is it 100,000 years? Well, 100,000 years is slow

because that's the time it takes for this random walk to get the light out. But there's a relatively small, chance of the second stage of the fusion. So the fusion will start by putting two protons together, two hydrogen nuclei together. And then it's got to meet something else before it can progress. And that's actually relatively unlikely, so it probably just decays back again to the protons before it gets there.

So this happens in a very controlled way. So you've got the core, then we move out. We move out into a so-called radiative zone. Radiative, yes. Because radiation is what dominates there. Does much happen now? No, it's fairly quiet. The temperature is steadily dropping.

It's sort of Sundays is on the sun on. Yeah, yeah, okay, it's Sunday. The temperature is dropping. Right, let's go on with radio. The temperature is dropping steadily because the high-energy photons, the light, is interacting all the time, and every time it has an interaction with a bit of the material,

it comes out of it a little cooler. So it's a quietish zone, but the temperature is steadily dropping, as you move away from the nuclear reactions in the core. Is there any sense in which the core is changing from the time it became the sun that we know? Is it going bigger? Is it going smaller? Is it being more active? Is it less active? Is it less reliable? And so on and so forth. Has it been a steady state for the last four and a half billion years? No. No. There are several ways in which you can say it's not in a steady state.

First of all, clearly, it's using up its fuel. The amount of hydrogen is dropping, and therefore the actual distribution of the temperatures is slightly different. And the size in which the nuclear reactions is happening, the volume in which it's happening, is actually changing. Interestingly, the young sun that Carlin was talking about when it was first formed was only about 70% as luminous as bright as the current sun. And that has implications of what we know about what happens on Earth. Because if there's less light coming out, we receive less light.

and therefore there's a whole topic there. So the sun's getting a bit brighter as it ages and the distribution of the fusion inside is changing slightly. But on a grand scale, no, it's a very stable time. Carolyn Crawford, so we've got out of the call, we've touched on the radiative. Joan, can you tell us a bit more about that

and then go to the next zone, if we're seeing it as layers, which is quite useful, I hope, the convection zone. What happens there? It'll be the radiative and the convection zones. Right, so as Yvonne's described, you've got the problem that all the energy is produced right in the core. That's the only place it's hot and dense enough to do this nuclear fusion. You've then got to get that energy out through the rest of the star to the surface so it can be escape away into space and travel towards us.

And beyond the core, you have, as we've just talked about, the radiative zone, where the energy travels almost like a slow pass the parcel between all the different particles and the gas, passing on the photons of energy. and that is efficient out to probably so carrying on the idea of fractions of distance out from the sun out to about seven-tenths of the sun's radius. But at that point the gas of the sun has cooled down enough that it's now in the form of atoms. And the thing about atoms is they're much more efficient about absorbing energy. It's like the past the parcel stops and they sit there and they hog the parcel.

And the gas heats up and you can no longer move the energy on in that way. and instead you have what's called a convection zone. And this is where you build up circulatory currents. It's a vertical rising of hot kind of gas, reaches the surface cools and then it sinks back down. And it's very similar to what you might observe if you're watching water boil in a pan. You're transferring the heat from the bottom of the pan

up to the cooler surface. So it's physical eddies of gas that are rising and then reaching the surface and sinking back down again. and that is a mechanical way of transporting the heat energy up to the surface where it can then be radiated away. So we're getting near to what could we call the surface. Are we? Yes.

Are we? So the next zone is like the thigh bones connected to the end. Anyway, never mind. The next zone is known as the photosphere. And it's the surface of the sun that we can see from the earth. Can you tell us about the photosphere on what you insist on calling this boring star? I'm finding fascinating. The photosphere, as you say, is what?

is the first chance we get to see what's going on in the sun. And there are two main things that we can tell from the photosphere. The first is if you look at it in detail, you'll see these wonderful confection cells. So Carolyn has described the confection process. We see evidence of it on the surface. So you see these confective cells where the plasma is coming up and then it's falling back and cooling. The scale sizes are small in the sun, but for us,

A sort of small confection cell would be maybe a thousand kilometers, so between Lanz End and John O'Grote's kind of distance. Then you have different size scales of that confections because it's... And what's happening there? The plasma is being brought up. It cools, it falls back down again. It's very chaotic, and that will allow the creation of magnetic field to occur as well because you've got these electrons being moved around,

and if you've got a if you cycle at all and you use a bike light, and you've got a dynamo on it. It's the same kind of process as working there. So the dynamo creates magnetic field. You can get the other feature that you'll see in the sun are sunspots. So at the minute we're close to solar maximum activity. So there are sun spots around and those will look like blemishes on the surface. So they'll look like, that's why they're called spots.

They look like spots on the sun's surface. And you can see those today. that there are these spots and those the reason why they look dark is because they're very very strong magnetic field and that holds back the confection so it holds back the plasma from coming up and those are the regions where a lot of activity comes from so those are regions we're really interested in but if you if you look at the surface and you analyze the sunspots the other quirky thing about the sun is that it rotates differentially so it rotates faster at the equator than at the poles.

Because it's a big ball of gas, it has this weird way of rotating, and you can measure that through measuring the sunspots. So it goes faster around the middle than it does at the top or the bottom. Which be hard to imagine on the earth. It's like something crazy sort of dance, right, isn't it? So you've got that happening, and you've got the convection. It's churning all the time. It's moving weirdly all the time, and that drives a lot of the activity that we see on it.

But the photosphere is what people have been observing for quite a while. Is that right? Yes. For how long a while? I mean since before Galileo or since Galileo and Kepler. Most observations have been made since the development of the telescope where you can actually observe the sunspots consistently. So they've been observed for hundreds of years,

which has allowed us to observe this cyclic behaviour that we see. So, Yvonne, since we were talking about the core. We've clawed our way up from the core to radiative, to convection, to the photosphere. Is there any further to go? Oh, yes. Louise would say this is the bit that's not boring. You're stuck with that. I can work with that.

Okay, so I was saying how the temperature just steadily drops and it gets cooler and cool and it gets to the surface which is at sort of just under 6,000 degrees. And then suddenly something strange happens. The temperature starts to go up again, totally counterintuitive. So you have a region known as the chromosphere where this sort of transition happens,

called chromosphere because it's coloured and people can see it at eclipses where the majority of the sun is covered, but you can see this thin outer layer and it's sort of pinkish, which is actually a colour associated with hydrogen. And then beyond it is what's called the corona, which is incredibly hot to back up to a million degrees or more.

So what's happened? Energy has been put in, I guess, is the obvious statement. You mean you don't quite know when you say guess. No, it's a physical principle energy must have been put in and therefore what one seeks is the energy. The current thinking is that this comes from the magnetic fields that Louise mentioned and when they north and south cross,

they neutralise each other and throw off a lot of energy. There are other methods put forward, some of which we may discuss later, like sound actually can be important, but in general I think the current thinking is that it is the magnetic fields that cause this rise in temperature. And then we don't actually run out of the sun. It just gets thinner and thinner, less and less and less denses you get further away.

And it then becomes a matter of definition as to when you say you've left the sun. Yes, the corona, it's a powerful part of it, isn't it? Because that's what sort of beams the stuff to us. Yes, absolutely, absolutely. And that's the areas where matter can actually escape and produce the solar, as it's called. Well, can you, Carolyn, can you take it up there? And tell us a bit more about this magnetic field

which seems to come in on the last lap and speed up the race in the last hundred yards. What's going on with, you've described it, of course you have, but I'd like, if you could do it more for somebody like me who got it, but would like more. Well, you have to think of the sun as how, I mean, the whole of the sun has a very strong magnetic field and it looks, where it erupts from the surface,

it's kind of like your standard bar magnet that you may remember sort of playing with in physics at school and it's got a north pole and a south pole and then you get magnetic field lines joining the two. But the magnetic field traces all through the sun and escapes out into space. So first of all, the magnetic field is generated, as Louise says, by dynamo.

You have some residual magnetic field within the sun maybe from that cloud that collapsed from the interstellar medium. You have electric charges in the sort of the plasma, the hot gas that's the sun. as they move through the magnetic field, you generate electric current, which in turn amplifies the magnetic field. So you have a case of that this magnetic field is continually regenerated by the motions within the star.

Somewhere we think between the radiative and the convective zone. So that's your global magnetic field. And when it escapes the sun, it also pulls some of this ionized gas with it. So Yvonne was talking about the corona. That is where the sort of atmosphere of the sun no longer is a sort of nice round shell. but you've got material pulled into long streams. It's such low-density gas that it kind of follows the magnetic field lines and is traced by them.

But you have this global magnetic field, which is incredibly strong, much stronger than you get at the Earth. But again, with magnetic fields, they're a fantastic way of storing energy. You can kind of pull them, compress them, you can stretch them, you can tangle them. And in the same way you can sort of stretch or compress a spring or rubber band, you can store energy in it and then when you release that it goes back to a natural configuration

and you get a huge input of energy like pressing a spring down, taking your hand off it goes or stretching your elastic band and then letting it go so there are ways which magnetic fields will reconfigure to much much kind of simpler configurations and then it releases all that energy

in one go and a lot of this is what powers some of the extreme behaviour we see in the sun and also whether you get that sort of localised twisting you know, from rotation of the sun, from this vertical motion with the convective currents, that's where you get the kinks and the knots, and that's where the exciting stuff, such as the sun spots

and the sort of real localised activity on the sun's surface builds up. Do you want to come in? I saw you're making a note. No, no, no, no, no. I was just thinking that the concept of elastic bands is actually really good because the magnetic field does get moved around and stretched and then sort of releases all that energy. And there are the big scale that you were talking about. But there's also, it all happens on a tiny scale as well,

sort of so-called microflares. So there's a constant little niggle of energy in as well as these great big outbursts that we see. So it happens on very many scales, which is one of the really interesting things about it. Well, let's continue this. Lewis Harrow, the sun's magnetic fields as we've heard, but it's

responsible for a number of phenomena. Can we talk about, which can be seen from Earth? Can we talk about sunspots and flares? First of all, can you? You've mentioned sunspots already, but just say a bit more about them and then flowers, please. Sunspots are, as was mentioned, the sort of dark blemishes that you can see in the

photosphere, and they are regions of very strong magnetic fields, so the strength would be sort of thousands of times higher than the earth's magnetic field, for example. So there's strong. The magnetic field will be complex. You'll have magnetic field emerging in from below and whacking into it and it will rotate and it will turn and it will create the energy that Carolyn is described. And that energy is known as a flare. So it's releasing fast amounts of energy very, very quickly in minutes. And that will, we can measure that in different ways. The

electromagnetic radiation will reach us within minutes that can heat up the earth's atmosphere. Particles will be released as well. The field lines will essentially just squeeze the particles, so we'll jet them upwards. So you'll get that effect too. You also get associated sometimes with flowers' coronal mass ejections, so you'll get a lot of material being ejected out into the heliosphere, and that can reach us too, and that will take a few days to get to us, if it's Earth-directed. So there's a lot of different ways energy can be released through the magnetic fields.

Is there any sense in which in the time you've been able to record this in more detail, you've seen significant changes in the behaviour, let's call it, of the sun? The sun has activity cycles, so we

roughly have an 11-year cycle and during the space age, if you like, and where we've been able to observe the sun in detail, the activity level has started to decrease so that activity has dropped a little bit so it would go through these short-term cycles and then longer-term cycles as well

Immon can you go into the cycles in a bit more detail? Yeah there have been sunspots on the sun is a very obvious measure of the magnetic field and what you see is that at times as Louise has said there are lots of sunspots and we've just well we're just going through maximum at the moment so there's lots of spots on the sun and then we go into a phase where there's

no spots on the sun and then the spots come back and they build up and they go away and it keeps on repeating and that's due to the magnetic field being actually created and then destroyed which is quite a neat concept so at times it's like a bar magnet as caroline said but why did you do it so regularly between sort of eight and 15 years it gets created and then destroyed what it seems to what's the internal mechanism that makes it do with that? It was like a clock. Do you want to become a physicist who deals in how the sun works as magnetic field? People disagree about it.

It's not really understood. Nobody can actually produce the periodicity without putting something else in that sort of forces it out. So it's something that those who model magnetic fields would really like to understand, but we don't. And as Louise has said, it's not only just that. there's this roughly 11-year cycle, but there are longer-term cycles. So there's a cycle that's around 100 years. So the maximum we've just gone through

is actually pathetic in a grand scheme of things. You certainly talk up your subject, I don't know. I'm saying, you'll big it up like anything. It's such fun that it's pathetic because... There have been times in the past when the sunspots all disappeared. You talked about...

Galileo at the beginning. Just around the time when Galileo was getting himself into trouble for talking about sunspots, the sun went through a phase where it had very little in the way of activity on its surface. And associated with that was really cold weather in northern Europe, famine, social unrest, all sorts of other things. So actually, given that we've gone into a period where the sun is getting quite quiet, We'd really like to understand what's going on. If it were just repeating regular as clockwork,

then I'd declare it much more boring. I think it's really quite fascinating that it's gone into this quiet patch. We've given a job, boy, we've given enough grief for that, fine, exactly. So, okay, so the sun now is roughly like it was 100 years ago in terms of its activity level, about half what it was a couple of cycles ago, at the maximum. and the previous minimum was very quiet, very spot-free, very long. Some of the indices that we used to actually measure activity

went to levels that we've never seen before. But egotistic humankind, which is listening to this programme, including me, I'm listening, they want to know what effects this solar activity has on us. And that can be major. Yes. Okay, it's low probability but high consequence events. if one of these coronal mass ejections, so as Louise has described,

if the sun gives out an enormous eruption of gas, and you've got this large sort of bubble of hot gas and all magnetic fields associated with that travels through the solar system. And if that hits the earth head on, you have what's known as geomagnetic storm. The magnetic field within this plasma will interact with the magnetic field of the earth.

There's rapidly changing magnetic fields. and it can induce enormous electric currents here on earth that could potentially be quite catastrophic. Now, we have had examples of this actually occurring in March 1989. There was a geomagnetic storm where some of these induced electric currents chose to travel through power lines

instead of through the ground and sort of took out the power grid in Quebec for about nine hours. There have been other examples just two years, years ago, enormous clouds of plasma that just missed the Earth by about nine days. They moved through the place where Earth had been just nine days previously. What would have happened if it had hit Earth? Well, first of all, the satellites that are just outside the atmosphere are going to be

quite vulnerable. There's a very sensitive electronics could get damaged, both by the radiation and the cloud of plasma. You have the potential disruption to the power grids, which is one of the major things. and if it really hit with no notice and damage the grids, it could be millions, probably billions worth of pounds of damage and take a while to recover from. So that's the sort of, as I say, low probability, but that's the kind of event we want to be able to predict and avoid.

And probably the best example of, you know, the danger that such events can bring actually dates from about 150 years ago there was an event called the Carrington event. It happened in 1859 where a British solar astronomer, Richard Carrington, was actually looking at the sun. He was doing all these daily measurements of sunspots that Yvonne's described, tracking the activity of the sun.

And he saw a couple of bright flashes of light on the sun, which then faded over the period of a minute. And, you know, this was very exciting to see something happen on the sun, which, you know, it changed on such a small time scale, hadn't been seen before. But the consequence was that 12 hours later, you had one of these geomatic magnetic storms where this huge bubble of gas

that reached the magnetic field of Earth. There were aurora all round the skies. That's another indication of when that you get an interaction between the solar wind or the plasma from the sun reaching the earth, bright enough that apparently you could read newspapers by them. And normally you see this just in northern polar and southern polar latitudes.

This was going down as far south as Bermuda and Hawaii. Again, if you see them far south, an intense storm. And the electric currents would travel along telegraph lines. So you have stories of telegraph operators who, unfortunately, some got shocked. Some telegraph officers were set on fire by these currents.

But they could also, it disrupted the telegraph lines in some cases. In other cases, they disconnected the batteries and found the telegraph lines were working better than ever with these electric currents from the storm. So you have these huge effects from the storm that long ago. can just see that if a similar event hit us now, we're much more vulnerable to this kind of

electrical disruption. Can you tell us, Louise, can you tell us something about the solar wind? The solar wind is, we've sort of touched on it already, but it's always there. We have a wind coming from the sun all the time. The speeds are large. They range from a few hundred kilometers per second to around 2,000 kilometres per second. So that's, you know, 100 times the speed of a transatlantic passenger plane. So they're fast. Basically, electrons, magnetic field, being sent out into the solar system. We've talked about the effect on us, but they affect all the other planets.

So it's been measured at Venus, at Mars, at Jupiter, at Saturn. And it's even been measured by Voyager, which is now at the edge of the Earth. the solar system. So the solar wind is strong enough to go for extremely long distances. It is variable and it does have an impact. So even the slower winds, the less dramatic winds coming from features that are known as coronal holes. That's basically a hole in the solar atmosphere that allow stuff to get out quickly. When those appear, those will have speeds of 800 kilometers per second and they'll be steady and they'll just keep on churning

and I know it's going to have a big effect as well. Will they have an effect here? They'll have an effect and something like that can have effect on spacecraft. So as we were talking about already I think we're so reliant on spacecraft and I use spacecraft every day. I'm sure when you buy

something in the shop with your debit card or anything like that we're all using spacecraft to communicate. So we're much more reliant on things like that now when you're travelling in an airline. You know, routes have to be diverted. Transatlantic routes or polar routes are diverted

because of lack of radio communication. So we're affected more and more because we're so reliant on these technologies. Yvonne Ellsworth, you mentioned earlier on that the importance of sound waves which are now involved. Can you develop that? Yes, absolutely. We've talked about convection

and the fact that you can see the convection process material moving if you boil a pan. I'd sort of carry that on and think, okay, if you boil a kettle, how do you know when you're about to get your cup of tea? Well, the answer is you can hear it. The kettle starts to make a noise.

The water moving becomes noisy. So if you have convection associated with that, you have noise, which is sound. And unexpectedly, people discovered that the sound that we all expected to be generated in the sun actually can travel through the sun. So it doesn't get destroyed and just confused

in the local region where it's produced, but it actually can travel. And it can travel right through the volume of the sun and set up resonances like a musical instrument inside the sun. So we have this sun where we've talked about all these local phenomena on it. We've talked about sunspots and players and all sorts of things. but you can also think of it as a big spherical body that gently breathes with a period of about five minutes

as the sound waves propagate through it and cause the surface to move just a little bit. And that just a little bit enables us to actually observe rather than conjecture what's inside. It's astonishing, isn't it? It seems. Yeah. Right, let's make.

Carolyn, we're... We've been able to see the suns from space in the last few decades. What's that brought to the information centre, which you three are? Well, we've talked about sort of the outer layers of the sun, the corona. The gas there is that the temperatures are like 2 to 3 million degrees. It's very faint in visible light. You can observe it very clearly using x-rays, and you can't observe x-rays from the surface of the earth.

So if you want to look at the sun in bands like x-rays, ultraviolet, there's lots of energetic activity going on within the flares, within the corona. You really need to do that from a satellite. And the other thing about a satellite, of course, is that it gives you a different vantage point from just being on Earth or around Earth. You can move satellites. For example, we've got a couple called stereo. One is just ahead of Earth in the orbit, one that's just behind Earth in the orbit.

And they give us a much more three-dimensional view of some of these mass ejections and especially how they might impact Earth. So again, it's the extent. viewpoint as well as the different wave bands. Okay, so Carolyn's passed out over to me. I needn't point to you. I needn't point to you. Obviously, you would pick up the battle. So we have stereo, as Carolyn described. So they are, they have a lot of us for the first time to get a 360 degree few of the sun. So I suppose like every small child is curious,

you want to see behind the things, you want to look down on them, etc. If you get that 360 degree few, then you can know that there's a nasty, big, complex sunspot that's about to come around. We want to know whether it's likely to erupt or produce one of these explosions. So we've got a better few if that was stereo. The other missions that we use are Hanode, which is a UK-Japanese US mission, which is basically like a microscope, so it's looking at the detailed physical processes. We have the Solar Dynamics Observatory, which allows you. you to have continuous monitoring,

which is another really useful thing about being in space. If you're on the ground, you've got nighttime, and you've got weather effects that you can't really avoid, but being in space, you avoid all that. So the continuous monitoring allows us to observe all those dramatic

changes that are happening. Yeah, and I'd like to follow up on the concept of seeing what's coming round, what big active region or flare or whatever might be coming your way. the magnetic fields, the sunspots and so on, actually influence the sound waves and it is actually possible to image through

to the back side of the sun and see that there is an active region forming on the backside and as the sun rotates in about 26 days so you get five, ten days notice about this object coming around and it's routine monitoring now it's done from one of the satellites

that Louise mentioned STO It's also done from the ground. So it's all geared to trying to make sure that we know what's about to happen and are not caught unawares. You're working on this. What is the most... Briefly, I'm afraid, sorry.

What are the most significant current developments in study of the sun? Understanding the details of the magnetic field, I think, is the biggest thing because the different instrumentation we have have allowed us to see the twisting see the shearing, measure that quantitatively, be able to understand

what will trigger a solar flare or a chronom mass ejection. So to get a grasp of the physical concepts around that, we've been able to do that recently. Is this new stuff currently, is this new information that's being pulled in? Is it changing

significantly views of the sun, say, 50, 100 years ago? From 50, 100 years ago? Yes, because we're understanding from the heliocysmology that Yvonne's described, the actual structure inside the sun, and we're understanding the actual processes about the flares being produced and the things that, you know, can have an effect on us here and earth. We're beginning to not just

understand them, but hopefully one day actually begin to predict from this monitoring to know in advance when and where a flare might occur, hopefully also how strong it might be, and start to do also that longer range forecasting with the solar cycles that we've mentioned. Then all of this is now within our grasp, we're not there yet, but this is part of what we're all driving towards. Anybody, we start with Yvonne. We've been told the sun's been around for four and a half billion. Our sew years, how much longer has it got to go?

Will it see us out? Yeah. You can rest assured on that. In terms of its current life, lifestyle, it's here for as long again. All right, so we're about halfway through. And then it becomes a different sort of star. It becomes a giant star, and that's probably curtains for us, actually.

It'll get a bit warm, a bit toasty, and we'll get enveloped in the sun, and it won't be nice. But you were asking what the developments are. The other thing I would chip in is we're now starting to study other stars through their interior sound waves. And that helps me answer your question. Very good. And that helps me come to the end of the programme.

Thank you very much to Carolyn Crawford, Louise Harrah and Yvonne Ellsworth. That's the last in this current series of In Our Time. We'll be back on September the 25th. Thank you very much for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests. Well, thank you all very much.

Thank you very much. last point about the other stars. I completely went from my... I'm so glad you pulled that out of me. I wanted to get it in because it isn't so interested. That was the first thing I thought and I was like, oh no, I'll start closer to home and then work out to the rest of the stars. And by the time I got there, he'd be gone. In those stars are right.

That's the other thing we were talking about, that we keep calling the sun boring, but that's because these other stars produce much bigger flowers and bigger chronomass ejections. Well, a little can be interesting. I mean, you sort of proved that. This tiny little sun that we're talking about were sufficient for a fairly packed conversation.

We thought our solar system was understood and worked out and everything, it was the paradigm. But actually it didn't turn out to be like that. And when we're doing this seismology and other stars, it's actually quite hard to find other stars that are so-called solar twins, just like the sun. So I wouldn't be surprised to find that if, you know, when you hold this in 10 years' time

and ask folks about the sun, Actually, it turns out not to be quite as usual and ordinary as we think. So we might be back to the uniqueness of our condition argument. We might be. Yeah. There's all sorts of... There are selection effects. It's actually quite tricky to measure stars like the sun

because it's easier to measure a nice big giant stars that are bright. But I'd be prepared to wager that it might not turn out to be average. So what did we massively miss, Caroline? Where did we miss? I do you know, I think we covered an awful lot of ground. Yeah. It might have been, didn't quite have enough time for you to expand about the red giant, but you've got in there.

I got my... The eventual demise of the, you know, sort of after that, that it, after the red giant, it sinks down to become a sort of white dwarf, so you've got half the mass of the sun compressed down to something about the size of the earth. It must be fun to think up names, wasn't it? Who had the fun of thinking of the red giant and white dwarf? They'll stick and we'll always use them. Do we know the person or persons?

Not always. Sometimes, you know, people who, you know, if things have happened more recently, then you do know who's coined the phrase, you know, so it's like Fred Hoyle with a big bang and I can't remember other examples, but the things, they're fairly descriptive. You know, dwarf because it's small and white,

because it's bright and it's hot and it rigid. I mean, never mind. There are those who argue about the roots of the words. Heliosysmology is the seismology of the sun but it's a mixture of Greek and Latin roots and there are those who get very upset about that and astro seismology is the same thing for the stars but I think that is properly

It's slightly your own fault as scientists isn't it because when you started naming things you gave it you were way behind classical learning in the area of respectability and so you tried to sort of show you just as good as them by clicking on Greek words, Roman, as a second from the very beginning.

Isn't that right? I think it's a good premise. I haven't got the evidence to argue it properly with you, but it's a good premise. I mean, had the advantage of being sort of super vernacular, didn't it? Because if you said Helio, people in Italy would understand it as well as people here. The etiquette people would.

So that's a serious advantage. Sometimes there are nice sort of consequences. So I've just been reading in one of the books who recommended about how asteroid means it'll start. And that was coined by William Herschel to do down the discovery. You know, he discovered Uranus in 1781, and then it was the turn of the 19th century, so the early 1800s. The Italian astronomers started to discover the first asteroids.

They wanted to call them planetoids. And he really promoted this name asteroid and pushed that they called asteroids to kind of separate them, say, you know, he's the only one that's discovered a new planet. these can't possibly be planetoids and he pushed this name where he stuck which if you think about it doesn't actually make much sense

Planetoid is much better Planetoid makes much more sense Well it's true But he you know he had this There I say well it comes across as this idea That perhaps not that generously To be described in a more sort of dismissive term

You know little stars I think we do tend to be on imaginative these days in terms of what things are called. I mean, like the solar orbiter mission. It's called solar orbiter because it's going to orbit the sun. Will they not give it a fancy name like the Japanese do? No, that's special to Japan, I think.

The Japanese missions will be named things like solar A, Solar B, Solar C, which is very boring. But after launch and this one successful orbit has occurred, then it's christened, essentially. So you're having no day, which means? a day means sunrise. Sunrise. Yoko, a sunbeam. It's much more poetic in a way, isn't it? It's lovely. Well, enter Tom Morris, producer with and at end of chat.

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