The science behind the aurora - what causes the Northern Lights?

Sun spots, solar flares and coronal mass ejections

To understand what makes the Northern Lights happen, we first need to explore what takes place on the surface of the sun. The sun is a massive, spherical star that’s right at the heart of our solar system, providing the energy that ensures there’s enough energy to sustain life on earth . It’s made of hot plasma and is composed mostly of hydrogen as well as helium.

Sunspots occur on those parts of the sun’s surface that are a little cooler than the rest. They’re found where the sun’s magnetic field is stronger, because this acts as an inhibitor for the hot gases at the sun’s core and impacts their flow to the surface. Sunspots appear dark and typically are created in pairs. It’s possible to see these from earth; the largest one’s don’t even require a telescope, though of course protect your eyes effectively if you’re trying to see them.

Sunspots are also where you commonly find solar flares and coronal mass injections. When electromagnetic radiation is emitted from the sun, we call it a solar flare. This energy can also cause coronal mass ejections; during these events, plasma containing charged electrons and protons is thrown out into space.

How do solar flares and coronal mass ejections influence the aurora?

Solar flares and coronal mass ejections happen during what’s known as geomagnetic storms. In periods of intense solar activity, the earth’s magnetosphere is disrupted by a solar shock wave. The particles within it can travel millions of miles and some get tangled in the earth’s magnetic field.

This process funnels them towards the north and south poles, which is why auroral activity isn’t evenly spread across the planet but instead concentrates more in some places than others. The Northern Lights occur towards the Arctic, while in the southern hemisphere, the aurora Australis (Southern Lights) are the equivalent.

Countries like Iceland that are located at high latitudes offer an increased chance of seeing the Northern Lights as they are under the aurora oval more often. Though it’s occasionally possible to see the aurora borealis further south, this is only the case when the earth is being affected by a very strong geomagnetic storm. In contrast, you don’t need as high a Kp index rating to see the aurora further north, meaning in countries such as Iceland it is visible much more often.

Why do the colours vary?

During this solar activity, the particles interact with atoms and molecules, which causes a reaction to take place. They heat up and get what scientists call “excited”. When the gases calm down again, they emit light and this is what we see as the aurora. The difference in the colours we see when we watch the Northern Lights is mostly down to the presence of various gases.

For instance, green indicates oxygen; this is the most commonly seen aurora. Meanwhile the same gas can cause reds when it’s found at higher levels of the atmosphere. Pinks, purples and blues – the rarest – can signify the presence of nitrogen. Yellow is sometimes also seen.

Measuring activity

Just as we have weather forecasts that analyse data and try to predict what happens in the lower parts of the atmosphere, so too we have forecasts about what might happen in space. Geomagnetic storms are measured using a couple of different scales. You might see such solar activity measured on the G-scale, which runs from 0 to 5, or as the Kp index from 0 to 9.

The higher the number, no matter which scale you use, the greater its intensity and the more vivid and active will be the aurora. G5 storms are rare in comparison, but happen more at the solar maximum. Solar cycles last about 11 years; midway through, the sun’s activity is greatest.

Can you see the Northern Lights with the naked eye?

In today’s world, we’re bombarded with images of the aurora across the television networks and the internet. Many people have shared the photographs they have taken of the Northern Lights on social media; perhaps this is what’s tempted you to consider a visit to Iceland in the first place.

But we need to manage expectations, because the colours you see in reality aren’t always as vibrant as those on your screen. Auroras can appear a white-ish grey, though the higher the Kp index, the more chance you have of seeing their colouration. It’s a good idea to carry a camera or smartphone with you on a Northern Lights hunt to be able to appreciate the full spectacle of what’s going on above your head.

Is there a best time to see the aurora?

We’re approaching the solar maximum now. This kind of science is in its infancy, so astronomers have to hazard a guess at when the solar maximum might be. Only when the data has been compiled and then analysed can they say for sure it has peaked. But somewhere between 2024 and 2026, many scientists are suggesting, will be the peak of this particular cycle.

So in that respect, the upcoming autumn, winter and spring could be an excellent time to witness the aurora borealis. A number of other conditions need to be met too, however, and to see the Northern Lights requires an abundance of luck as well. But it’s worth persevering, as when you do catch a glimpse of them, they’re a fabulous sight.

For instance, you’ll need it to be dark; light pollution can wash out the aurora and make it almost impossible to see. Likewise, it’s a good idea not to time your Northern Lights hunt for a full moon night. You’ll also need clear skies. When clouds form in the lower parts of our atmosphere, they can block our view of what’s happening above, so it’s necessary to find at least a gap in the cloud to give you a chance to see the aurora.

Is there anything else you can do to maximise your chance of seeing the Northern Lights?

There appears to be a correlation between the equinoxes and the appearance of the Northern Lights. Statistically, they show up more often around this time in September and March. If you’re lucky enough to be in Iceland at this time and you’re blessed with fine weather, you potentially could have a greater chance of seeing the aurora.

But there are no guarantees, so make sure you have plenty of other plans for what to do during your visit so that you don’t put all your eggs in one basket. For instance, the Reykjanes peninsula has a variety of breathtaking natural landscapes, including those altered by geothermal and volcanic activity. Soak in the Blue Lagoon, visit the Bridge between Continents or hike to see old lava flows.

But after dark, always keep an eye on the sky and who knows, you might just see the magical Northern Lights for yourself.