Instant Genius - The science behind the stunning phenomenon of the Northern Lights

Episode Date: April 3, 2025

The Northern Lights are surely one of the most awe-inspiring phenomena anyone can be lucky enough to witness occurring on planet Earth. But how exactly do solar winds breezing out of the Sun and hitting our planet’s atmosphere create the enchanting phosphorescent display that dances across the night sky? In this episode we speak to Tom Kerss an aurora chaser, astronomer and author of the book Northern Lights: The definitive guide to auroras about the science behind the breathtaking phenomenon of the Aurora Borealis. He tells us how the colours of the Northern Lights are created by particles ejected from the Sun hitting the Earth’s magnetic field, how auroras also exist on other planets within the Solar System and talks us through the many things we can learn from studying this fascinating cosmic phenomenon. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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The Northern Lights are surely one of the most awe-inspiring phenomena. Anyone can be lucky enough to witness occurring on planet Earth. But exactly how do solar winds breathe? freezing out of the sun and hitting our planet's atmosphere, create the enchanting phosphorescent display that dances across the night sky. In this episode, we speak to Tom Curse, an Aurora Chaser, astronomer, an author of the book, Northern Lights, the definitive guide to auroras. He talks to us about the science behind the breathtaking phenomena of the Aurora Borealis. He tells us how the colours of the northern lights are created by particles ejected from the sun. hitting the Earth's magnetic field, how auroras also exist on other planets within the solar system,

and talks through the many things we can learn from studying this fascinating cosmic phenomenon. So welcome to the podcast. Thanks very much for joining us. Well, thank you very much for inviting me. It's my first time to be on the podcast. I'm very excited about it. So first off, I think, could you introduce yourself and tell our listeners a bit about what it is you do? I can. I do lots of things, but I'll try to keep this one on topic. So my name is, Tom, I am Chief Aurora Chaser, which is a title you might not have heard before, but you can probably divine from the second two words what that involves, chasing the Northern Lights, which is at the top of almost every bucket list in the world, and is becoming more and more

popular as more and more people become aware of the extraordinary experiences that you can have by going up into the Arctic and coming under the Aurora Oval. So I actually lead voyages into Norway to take people to see the Northern Lights, but also to experience them on, as I see it, a deeper level. I've been chasing the Northern Lights myself now for over 17 years. I've had thousands of sightings over hundreds of clear nights, and I've been very lucky and privileged to experience all manner of different kinds of auroral displays. And one thing I've learned from all that experience is that every time you see it, it is like seeing it again for the first time. So I now make it my mission to help people see it for the first time so that I can, if Icarious

live through them as well, and experience this incredible moment that we're going through where the solar maximum has coincided with such a surge in interest, with sightings of auroras in very unusual places that have drawn people from all over the world to pay attention more to the night sky. So I take people to see the northern lights, but I also help them to understand it on a very deep level, and also share the Arctic sky itself, which means not just the auroras, but the stars, not just the stars either, but the stars that our ancestors and the ancestors of the Nordic peoples saw, the Sami people, perhaps, or the Vikings. So trying to add more context to that experience, I think it's a really nice way to be put in touch with nature.

And ultimately, to witness one of the great spectacles that can be seen on this planet, or perhaps even any other, which is the Northern Lights, which for my money is the most splendid thing you can see in the sky. Great. So let's start with the sort of obvious question then. What exactly are the Northern Lights? So the Northern Lights, it's an ancient term. It actually dates back to the 13th century, were first sort of named by Greenlanders and Norwegian explorers who travelled to Greenland. And they became aware of these lights appearing in the northern part of the sky. Much later, we had a term created by Galileo, which is Aurora Borealis. And Aurora Borealis translates to the dawn of the

north, and Galileo believed that what he was seeing in the sky, which we do credibly know he would have seen at least once from his home in Venice in the early 17th century, was in fact some sort of light being reflected off the sky, and that's why he thought it to be a dawn glow occurring in the north. But actually, we now know that the northern lights are an emission of light happening in the sky, and they begin their journey all the way over at the sun, 93 million miles away from us, where a constant outflow of charged particles called the solar wind floods the solar system. It escapes the solar atmosphere and eventually it finds its way to Earth, as it does with all the other planets and indeed escaping the solar system at great distances.

But that material, when it intercepts the Earth, it interacts with our own magnetic field. And if you close your eyes, you can probably picture the Earth's magnetic field. We sort of learn about it at school and we imagine a big bar magnet inside the Earth and these protruding lines that create this kind of force field, this bubble. And indeed, that bubble does protect us from what might be harmful effects of the solar radiation. But that bubble interacts with the solar radiation because the solar plasma, that is to say, the solar wind, it has its own magnetic field.

And when the two interact, there's a kind of transfer of energy where solar wind particles become trapped inside the Earth's magnetic field. So most of them are deflected, but some of them are actually sifted in. And as we have this sort of instability within the Earth's magnetic field, field, particularly on the side that faces away from the sun, which is a long tapering region, we call the magneto tail. We can have these magnetic events that inject a huge amount of energy into that idling solar radiation, that plasma, those electrons, let's say, and give them a boost and essentially fire them down into the upper part of the Earth's atmosphere, but only where

the magnetic field is at its most dense, which is around the two geomagnetic poles. So we have these large electric currents pouring in to the Earth's geomagnetic poles in two large rings, two large ovals. And then the second stage of this phenomenon occurs when those solar electrons interact with gas atoms in the atmosphere above our head. But to be clear, the atmosphere I'm talking about here is very high, hundreds of miles above our head. We're really talking about the ionosphere, which is practically a vacuum. It's nothing like the air that we breathe. So there's an abundant amount, but very sparsely spread of atomic oxygen and also some molecular nitrogen as well, but largely it's atomic oxygen which is interacting with those electric currents, those

electrons pour down through the ionosphere, kind of precipitating, forming a large current, and as they give energy to the gas atoms, a process called excitation, eventually the atoms give the energy back in a process called emission. So those gas atoms will hold on to some of that energy in the form of an electron which is excited. And when the electron returns to its previous state, it gives back some of the energy in the form of photons. And the exact energy that it gives back determines the colour of the photons, red in the upper part of the auroral curtain from very sparsely spread oxygen atoms. This is a low energy emission. And then green further down in the curtain, which is a high energy emission from rather overexcited oxygen atoms and atoms that

interact with each other after just a few seconds, taking the opportunity to give back a larger amount of energy, which is to say a photon more in the green part of the spectrum. So those are the two prominent colors. They're being emitted by gas atoms, which are energized by electric currents. And if it's all rather difficult to visualize, just think about a plasma ball. A plasma ball works in the same way. You've got a globe with neon and argon in it, and you've got an electrode at the center. When I was a kid, everybody wanted a plasma ball. I mean, that was in the 80s. So it was the coolest thing you could have back then. Nowadays, you can get them off the internet for five bucks. And, you know, they might electrocute you, but I'm sure it's fine.

Anyway, the electrode in the plasma ball is pouring this electric current out through the gas. And when the neon absorbs some of that energy, it gives off red light. And when the argon absorbs some, it gives off blue light. And if you put your finger on the edge of the ball, you can make a brighter arc. So really, you're playing the role of the magnetic field there. You're creating those bright arcs, just as the Earth's magnetic field focuses that radiation. And then it is the electrons themselves exciting the gas atoms, causing them to glow. So the Earth is kind of like a big plasma ball, but the plasma is coming from the sun and interacting with our ionosphere.

So you mentioned there the different colours, but another distinctive feature of the aurora is it's sort of almost dance-like movements. So what's causing that? That's a good question. And it's actually somewhat at the forefront of Aurora forecasting science today, because it's something of a mystery. The aurora is a visible expression of something we otherwise wouldn't be able to see, which are these large ribbons of magnetic flux, which are forming inside the Earth's magnetic. Now, that's an incredibly complex thing to model. It's a magneto-hydrodynamic situation. It requires supercomputing power just to figure out how the magnetic field evolves. But what we can say is that when the aurora brighten up and generally become more dynamic in tight curtains of bright emissions that

dance and flicker in the sky and wave around, that's where we have a particularly high amount of magnetic flux. And we might think of that as an increased amount of magnetic stress. And the relieving of that stress, it creates the motion that we see. The reality is that most of the dancing auroras we see are created as a result of events that occur inside the Earth's magnetic field, which we call magnetospheric substorms. And these substorms can be forecast with some level of accuracy, about an hour in advance, and we can see them going off with just a couple of minutes notice before the aurora is likely to become visible. They produce the short bursts of dancing that might last 15 to 30 minutes, where the aurora brightens up and moves

around the sky. But then there are many other kinds of aurora as well. And when you're up in the Arctic, quite often, if the aurora is not highly active, you can step outside and look to the north and see an ambient glow because the auroral oval is an ever-present structure, which is always receiving some energy. And if it's enough, it's actually visible to the eye. So you can have these kind of very diffuse auroras, and you can have very discreet auroras that are much brighter and move around very quickly. And there's just a huge number of different physical processes interacting at any given moment. But if you do want to give yourself good odds of seeing a lot of dynamic motion, then geomagnetic storms, which create very powerful hours-long periods of auroral activity,

they tend to motivate a great deal of this stancing because they're inducing a lot of stress into the earth's magnetic field, ringing the earth's magnetic field like a bell. And as that bell rings down and that energy is released, those auroras play. So you mentioned their forecasting. So how do we go about that? Now, forecasting is my game. It's one of the things that I'm intensely interested in, and we're living in an age where we have so much access to information, even as I speak to you. Recent research has been published, which uses machine learning models to analyze hundreds of millions of images of the Aurora from space and create statistical relationships with particular indices that we track.

And so this is a very fast evolving field. But there are, broadly speaking, three ways that we can forecast the Aurora. So it starts with the sun, and we can see events occurring on the sun thanks to a fleet of solar sentinel satellites. So we're talking about things like the Solar Dynamics Observatory and the Parker Solar Probe, which are able to directly observe the sun's lower atmosphere, where enormous amounts of energy are released into the solar wind from active regions. These are tied to what we typically call sunspots. So again, we're talking about magnetic stress here and the relieving of stress in some form. And when large active regions erupt, they can create solar storms, what we call solar flares,

that sometimes are followed by coronal mass ejections, which put a huge amount of material into the solar wind. We can also have what we call coronal holes, which are areas of the solar atmosphere where solar wind escapes at a very high speed. And so by looking at all of these different structures in the lower atmosphere of the sun, scientists, particularly, for example, at NOAA, the National Oceanographic and Atmospheric Administration in the United States, they're able to produce sophisticated supercomputer models which predict how the solar wind is going to propagate from the sun's lower atmosphere to where we are. Now, given that we're over 90 million miles away, that propagation time can be anywhere from 18 hours up to around 28 hours or 30 hours, depending on how fast the solar wind is moving. So that gives us a look ahead of a couple of days,

and that gives us time to really start thinking about how things are going to be in a couple of days. We can also think in more general terms about how things are going to be in the next week or so, if we look at objects or structures that are coming around the sun's limb and coming into our line of sight and are going to be spewing particularly interesting solar wind in our direction. The next time that we can see the solar wind isn't until it actually gets quite close to the earth. It has to get to one of the Lagrange points, which is about one and a half million kilometres from the earth. And so we have this look-ahead time of a couple of days where we're forecasting using models. But then the solar wind ultimately starts to arrive. And thanks to satellites like

discover, which are able to taste the solar wind 30 to 60 minutes before it gets to the earth. We then have a much shorter window of forecasting opportunity. And once the solar wind is about to arrive at the earth, we can start to measure its properties. So we look at the magnetic properties and we look at the plasma, that is to say the temperature, the speed, the density of the solar wind. And through a number of different relational algorithms, we can make inferences about whether or not the solar wind is going to improve the conditions for Aurora or inhibit them. Now, this isn't an exact science. We can't just say the solar wind is going to give us Aurora or it's not. It's a bit more like a sort of stock market graph. We're kind of tracking whether things are going in the right direction or not.

And if they're going in the right direction for a long period of time, then we become more confident that these magnetospheric substorms are likely to develop. So when I'm out forecasting in Norway, I'm constantly monitoring the real-time solar wind data, which is made available from satellites like Discover and Ace. and that's giving me a good idea over whether or not the next hour is going to be a good hour or a bad hour. And if I see that trend progressing for a long time, then I'm getting really excited. But the final step is what we observe actually on the ground. So we use ground-based magnetometers to monitor something known as the ring current or electrojet current, which surrounds the earth. And when this current starts to weaken and, if you like, become overwhelmed by currents within the magnetosphere, auroras are almost certainly going to occur just in the next few minutes.

So I might be looking ahead a couple of days to give me an idea of when the next opportunities are coming up. Then on the night, I'll be looking ahead about an hour to figure out how soon that's going to approach. And then I'll be looking at these geomagnetic ground stations, for example, at the Finnish Meteorological Institute, to look for sudden changes in the Earth's magnetic field, which indicate that a substorm is imminent. And we're probably going to see Dancing Aurora's in the next five minutes or less. So it's this kind of three-stage process, and the confidence grows as you get closer and closer to the event itself. Now more people than ever can bring in their bill for a better deal at Verizon. Got AT&T or T-Mobile?

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name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. So we have auroras on the northern part of the planet and the southern part of the planet. Are there any differences between those or are they essentially the same phenomena? Yeah, both the auroral ovals are similarly intense and it's not correct to suggest that they're mirror images of one another, but they occur with a similar intensity.

So if there is a storm force auroral forecast, you know, if it is an outlook for good storm force auroras, then we can rest assured that while the northern lights are exploding, so too are the southern lights. But there's a bit of a phenomenon with the geometry of the earth that people don't really think about, which is that if you take, for example, Australia, you know, Australia is about as far south as Spain is north, and you don't see the northern lights from Spain very often, and you don't see the northern lights from Australia very often as a result. You have to go really far south, and there's basically nowhere to stand except Antarctica, where you're routinely in view of the southern oval.

So for that reason and the fact that 85% of the population lives in the northern hemisphere, the northern lights tend to get most of the attention. But yes, they do occur in the southern hemisphere, similar colours. It's the same phenomenon occurring there. But of course, a drastically different view because you have very different stars, perhaps even a bright view of the Milky Way. So it's always been a dream of mine to see the southern lights and a dream I hope to make happen in the next few years.

So sort of coming off the back of that, Do other planets have auroras, or is it something unique to Earth? I love this question. So there are three prerequisites for auroras. You need some particulate radiation, so something that will generate a current, like flowing electrons or protons. You need a magnetic field, because the magnetic field actually takes that current and focuses it with enough intensity, gives it enough energy to excite gases. And then the third ingredient is, of course, the gas itself, the atmosphere, which actually emits the auroras. So it's no surprise that if you look at our solar system, you find auroras everywhere. Well, everywhere except Mercury. Mercury does not have an appreciable atmosphere. But once you hit Venus, you've got auroras on Venus, of course ours on Earth. You have strange kinds of auroras called proton auroras occurring on Mars all over its dayside and in pockets on the night side.

Jupiter has the most powerful and dramatic auroras in the solar system because it has a very strong magnetic field and a very intense radiation environment. But it might surprise you to learn that the source of Jupiter's particular. radiation is not the sun. It's actually the volcanoes on one of its large moons, I-O, spewing electrons into its own radiation environment, which are then accelerated within its magnetic field. Saturn has powerful auroras as well, and both Uranus and Neptune also exhibit auroras. We've even discovered auroras on some of Jupiter's moons, including Ganymede, where they were used to probe the interior and determine that it is likely that a large saltwater ocean persists there. And we've even found auroras in the atmosphere of comets like

67p Juryamov Gerasimenko, which became famous about a decade ago when a spacecraft, Rosetta, arrived there. We found auroras, in fact, in the atmospheres of strange stars, known as brown dwarf stars, kind of substellar objects. And we've even found Aurora as being generated in a coupling process between a star and its exoplanets using radio telescopes. So it turns out auroras are everywhere. And not only are they everywhere, they actually are starting to be reverse engineered as a kind of proxy for studying the climate. and environments of other worlds. So it may well be that in the long term,

the discovery and characteristics of some auroras are used to determine the climate of a planet that we think is habitable. It could be that Aurora is actually a one brick in the wall in the search for life. And that is only possible because of our interest in the auroras here on Earth and figuring out how they work,

that we can now reverse engineer the process and figure out what's going on elsewhere using remote sensing. So let's stick with that then. So what can studying the aurora tell us about things like the sun, the action of the sun, what's going on in the sun's core, maybe, what's going on in the corona, what's going on with the Earth's magnetosphere or ionosphere? What can we figure out from studying this? So one of the things I said earlier is that the aurora is a visible expression of something

we otherwise wouldn't be able to see. And truthfully, it's a visible expression of a lot of things that we wouldn't be able to see. It's an expression of the Earth's magnetic field. It's an expression of the solar wind and the makeup of the solar wind. It's also an expression of the composition and size and temperature and so on of our own ionosphere, which of course is always changing as well and is of interest to understand. So if we can look at the different aspects of the aurora, the intensity, the color, how they're connected to events on the sun, then we can start to piece together some of the unseen mechanisms behind them.

Like, for example, the composition of the ionosphere, what is actually. happening in this moment with the Earth's magnetic field, how common the magnetospheric substorms are, and also our interaction with the solar wind. And to give you an example, there is a phenomenon in aurora chasing known as the equinoctial effect, where many aurora chasers will travel to see the northern lights in the equinoxes, so around late September and late March, where there tends to be an uptick in the visibility of bright auroras or the development of substorms. And the reason for that is now tied to something called the Russell McFerrin effect, which relates to an increased kind of efficiency of transfer of radiation into the Earth's magneto tail

during the equinoxes based on the relative alignments of the solar magnetic field and the Earth's magnetic field. So these kind of unseen magnetic interactions are being revealed by studying auroras. We also are learning things about our ionosphere by studying phenomena that are related to auroras. You may have heard of the phenomenon known as Steve, discovered by Eric Donovan at the United States, University of Calgary, based on reports from amateur aurora chasers, particularly based around Canada. Steve is a sub- auroral ion drift phenomenon, so it's occurring within the ionosphere entirely, and as a result of that, there is some unseen ionospheric effects which connect intense auroral displays to this rare phenomenon. So there are kind of ongoing mysteries related to the

upper part of the Earth's atmosphere that perhaps the Aurora is one of the best ways to understand. And so for that reason, I think that scientific study into the Northern Lights is just inherently fascinating. I also know people who study auroras on other worlds. And as we just talked about, that can be a proxy for understanding things that are happening on other worlds. So there's there's kind of opportunities here to kind of take your interest in the Aurora if it fascinates you and use that as a tool in your arsenal of space physics to figure out what's happening, for example, in the atmosphere on Jupiter or in the subterranean oceans of alien moons. So basically there's really no end of mysteries that still need to be solved. We're really just

entering the golden age now where the Aurora is being studied with so many different angles that I think we're in for a very exciting decade ahead. Thank you for listening to this episode of Vincent Genius brought to you from the team behind BBC Science FACUS. That was Tom Kurz. To discover more about the topics we've just discussed, check out his book, Northern Lights, the definitive guide to Aurora's. If you liked what you just heard, then please do consider subscribing to Incent Genius on your preferred podcast platform. If you'd like to see our presenters and guests in person, then please also check out our

YouTube channel at ScienceFocus. The current issue of BBC ScienceFocus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your app store of choice. You can also find us on Apple News or online at ScienceFocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analogue warmth. Alongside French acoustic specialist vocal,

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