Northern Lights - what are they?
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Hello, it's Hannah Gelbart here and welcome back to another episode of What In The World from the BBC World Service.

Now, seeing the northern lights used to be a once-in-a-lifetime thing. The night sky lights up in pink and green, and of course, everyone rushes to capture it on their phones. And did you know there are also southern lights too? So today, we want to find out what causes these beautiful colours, why people are seeing them more often, and you're going to get tips from a photographer on how best to capture them.

Here with me in the studio to talk this through is Caroline Steele, a BBC Science presenter. Hello, thank you for having me. You're welcome, it's great to have you on the podcast. Yeah. So, have you ever seen The Northern Lights yourself? I wish I could say yes, and I feel like I should be able to say yes because I'm such a fan, but no, I haven't. I've tried so many times. So, a few times this year, I've driven to a field outside London and stood in the dark,

looking up at the sky, really excited, but I've not managed it yet. Have you seen them? I've also stood on my balcony and it's always just been kind of rainy and cloudy where I am. But I have seen loads of photos of them. For people who don't know what they look like, can you describe what you might be seeing if you see them with your naked eye? They can look absolutely incredible. So if you imagine a photo, I imagine most people have seen a photo of the Northern Lights. You know, you sort of get...

ribbons of light through the sky. It can be green, it can be purple, it can be blue.

It can look slightly different with the naked eye. Not that I know firsthand, but apparently they're slightly less bright because when you take a photo, you basically leave the lens of the camera open for a little bit longer to capture a bit more light. But they do also move and flicker, which is something you can only really see in person and doesn't capture very well on camera. And they don't look like they're that far away, but they're actually 100 to 600 kilometres above the surface of the Earth.

They actually start with the sun. So the sun is constantly emitting charged particles. It's sort of sending something we call solar wind towards Earth. So the Earth is constantly getting bombarded, kind of rained on by these charged particles. Luckily, the Earth has a magnetic field and it kind of looks like if you imagine the Earth, it's like the Earth has got two ears. That's the magnetic field.

And the magnetic field protects Earth from these charged particles. So normally we don't notice that we're being rained on by the sun. But sometimes these things happen called coronal mass ejections, which is where there's essentially a sort of explosion on the sun's surface. And it sends out a ton of charged particles towards Earth. And the magnetic field gets a little bit overwhelmed and some charged particles can get in at the North and South Pole.

And when these charged particles collide with atoms in our atmosphere, that gives off light. And that's why we see these ribbons of light in the sky. What causes the different colours? So it depends on what kind of atom the charged particle is colliding with. So if it collides with an oxygen atom...

you see green light. And if it collides with a nitrogen atom, you see kind of bluey, purpley, pink light. And normally we see green light in the northern lights. And that's because it's actually kind of easier to excite an oxygen atom to make it give off light. It's a bit harder to do that with a nitrogen atom. So it only looks sort of blue and purple if there's a huge amount of charged particles kind of raining down on Earth. And I sort of noticed that we are dressed like the northern lights. LAUGHTER

So I'm like an oxygen atom. In your lovely green jumpsuit. In my green jumpsuit. And you're like a nitrogen atom in your purple top. So you're basically like a huge coronal mass ejection display. I've never been called a coronal mass ejection before. I'm a smaller coronal mass ejection display. So great compliment, I know. Yeah, I will take that one. I'll hold on to it. Yeah.

And what about the sound they make? Apparently you can hear the coronal mass ejections too. Yeah, so this is something really interesting. And actually scientists have only worked out what's going on recently. So, you know, hundreds of years there have been reports of people saying the Northern Lights also make a sound. But they were generally kind of dismissed as, you know, misremembering or perhaps it was rustling in trees or something like that. It was sort of thought, you know, they don't. People think that it does, but it doesn't.

But recently, scientists in Finland basically recorded the Northern Lights over a long period of time and found that 5% of the time there was this sound associated with the display. And they noticed a pattern. So you're more likely to hear them when it's been a warm but mild day.

So the theory behind this is that on a warm day, you know, the surface of the Earth and the air around it heats up and then as the sun sets and it cools, this warm air kind of expands away from the Earth and creates this kind of bubble, this layer.

And the scientific theory is that it's the interaction between the northern lights and this warm layer kind of creates static charge. And it creates a kind of crackling sound like white noise. Are they becoming more common and what's causing that? So it's kind of two parts to that. So right now we're in what's called a solar maximum, which basically means the sun is at its most active and the sun has an 11 year cycle.

So it's sort of right now it's more active, then it's going to become less active. And in another 11 years, it will be more active again. And that basically means there are more of these coronal mass ejections. There are more kind of big explosive events that emit charged particles. So that means that there are more displays and you can see displays further away from the poles.

But there's also something else which I think is kind of contributing to more people seeing them, which is more people have smartphones. We're more interconnected. You know, I'm on my local Facebook group. And if anyone sees the Northern Lights, everyone will be posting and I will get up off the sofa and leave my living room.

and go and have a look and maybe be able to see them, which might not have happened 11 years ago. Where are the best places in the world to see them? So ideally you want to kind of be as near to the Arctic Circle as possible for the northern lights. So places like Iceland are really good, Norway, Scotland can be good. And if you want to see the southern lights, then ideally you want to be in Antarctica. Obviously that's quite hard. But big displays can be seen in South Africa, New Zealand, Tasmania, Australia.

What do the southern lights look like? Are they as impressive? Yeah, they can be just as impressive. I think the reason why we sort of hear about them a bit less is fewer people live on land around the South Pole. So if you live in Antarctica, you have a great chance of seeing them, but not many people live in Antarctica. And then you actually have to go quite far to get to South Africa, to New Zealand, to Tasmania,

Whereas in the Northern Hemisphere, you know, places like Iceland are really near the Arctic Circle. So there's just more people that are kind of in the place where you could see them. You know, there are some places where you stand a better chance. So, for example, you don't want to be near light pollution. You don't want there to be cloud cover because that blocks them. Ideally, you don't want there to be a full moon. So...

all these kinds of things can increase your chances of seeing it. It sounds like winter might be a better time to see them when it's a bit darker. Is that the best time of year to go? Yeah, so in the northern hemisphere, it's November through to March, where, you know, yeah, it's winter, the nights are longer, the nights are darker. And then for the southern hemisphere, it's the opposite of that. So I think it's

something like March through September, which is their winter, that's when you stand the best chance of seeing them. And maybe you are in a place that you want to go and see the Northern Lights and you want to take a photo of them. If you do, here are some tips on how best to capture them from a photographer, Hugo Kordhonen, who is 21 and from Finland. I see the Northern Lights quite a lot as I get to live in Finland and here they are pretty frequent.

Yeah, the experience is magical. Sometimes you might not even be able to actually spot it with your own eyes. They can at first seem like clouds, but then when you take a photograph of the sky, then you might notice the greenery after all the lights. But then at the best case scenario, they're absolutely incredible. And they just like dance in the sky in every direction.

It is an experience that I believe everyone should experience at least once in their lives. It's amazing and you lose the track of time and stuff. It is wonderful. So my advice for those who are looking to capture the northern lights either on their phones or the cameras, like bigger cameras, would be the following. So if you do have a night mode on your phone, please consider using that because that's going to help you get higher quality photographs.

And then have a tripod. This is gonna allow you to have longer exposure times, which is gonna lead to also better quality photographs, because the more light that gets into camera sensor, then the higher quality the photograph will be. Then if you can adjust the settings, then please do adjust the ISO and the shutter speed and then the aperture.

The shutter speed often does depend on the speed of the Northern Lights, so there's not a setting that always is going to apply, but between 8 seconds and 1/4th of a second seems to do pretty well. Then don't be afraid to push the ISO up, because

Nowadays the cameras can handle ISO pretty well and you can also remove it in post-production and then have as low as possible of an f-stop number in order to get as much light into the camera sensor again in order to have a better quality photograph. Then when it comes to actually taking the photograph apart from the technical stuff I would like you to ask the question of what story

do I want to tell with this photograph? When it comes to the difference between a great nautilus photograph and then just merely a capture, there often is this, yeah, this thinking makes a difference. The idea of the photograph.

Are there any negative side effects of the Northern Lights, all of this magnetic field pollution or, you know, charged particles being bopped around our atmosphere? Well, we're really lucky that the Earth has a magnetic field because if it didn't, you know, life wouldn't be possible. They can be a bit of a pain in that they can interfere with radio communication between GPS satellites and with, say, the International Space Station and Earth, but, you know, nothing too major. You

In absolutely extreme cases, they can cause power surges. So there was this huge event in the mid-1800s where the skies absolutely lit up. There were reports of people getting up and getting ready for work because they thought the sun had risen. Back then, we weren't dependent on electricity in the same way as we are now. But we did have telegraph machines and some of those broke. Some people who were using them got electrocuted and they did sort of fire sparks. So there was a bit of a problem in Quebec in Canada where

In 1989, there was a huge display and that did interfere with the power grid a bit. But it's basically never happened on a huge scale. So we don't really know what would happen. There was a big coronal mass ejection in 2012 that narrowly missed Earth. So we did nearly just have one. I feel very small. Yeah. I feel very, very small. And when we talk about space, it gives me this sense of perspective.

Yeah, it makes everything seem insignificant, right? It's like I'm a tiny speck on a tiny planet that's being bombarded by particles from the sun. It just makes everything seem unimportant in comparison. Caroline, thank you so much for coming on the podcast. Thank you for having me.

Before we go, I just want to tell you about some of the other stories we have covered on What In The World, like about the banana that was sold at auction for more than $6 million. We asked if the price of art has gone bananas. We also look at things like when or if borderless travel in Africa will be possible. You can find those and all of our other episodes wherever you get your BBC podcasts or on YouTube on the BBC World Service's YouTube channel. Thank you so much for joining us. I'm Hannah Gelbart. This is What In The World from the BBC World Service.

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