Caoimhín's Content

Recently, the Aurora Borealis or the Northern Lights has been visible from the South of Ireland. This is thanks to a solar storm, so we will begin by looking at the Sun and move from there to the aurorae and how likely we are to see more of them. Although you should never look directly at the Sun, it can be observed with special equipment. One thing you may see is the corona of the Sun, extending around the sides, this is normally easiest to see during a total solar eclipse. The corona of the Sun is usually hard to see unless the light of the actual Sun is blocked, but there are solar telescopes designed to do that or otherwise highlight the corona. Otherwise it it mostly the disc of the Sun you get to see, usually with a scattering of sunspots. Sunspots are hard to predict, though details about their places and sizes have been recorded for some time. Depending on when you look at the Sun, you may see no sunspots at all, if there are few enough that none are facing the Earth. The variation from lots of sunspots to very few sunspots does follow a pattern, an eleven year cycle of activity.

These cycles begin and end with a low period of activity, and 2020 was the beginning of the last solar cycle. Back then, the Sun had very few sunspots or storms, and generally looked quite smooth. Over the course of the past few years, the amount of activity has gone up and up. The number of sunspots has zigzagged up and down a little, but the upward trend has continued and will continue until the current cycle of activity peaks, around 2026. That peak should see the most sunspots and solar activity, before the activity decreases again, eventually reaching another low point in 2030 as we move into the next cycle. The flares and storms often visible reaching out from the Sun can sometimes launch high energy particles far into space. Usually, a lot of the Sun’s storms are constrained by the Sun’s magnetic field, forming loops and arcs, usually around sunspots. The highly charged particles that make up the Sun are influence by magnetic fields. The Sun’s influence really extends all the way to the edge of the solar system, our magnetic field is essentially inside the field of the Sun, but that will have to be discussed another time.

We are constantly bombarded by high-energy particles from the Sun, but when a storm or loop breaks free of the Sun, a lot more can head towards the Earth. The Sun also sends photons our way, photons are pretty light, they have practically no mass. I won’t get into the physics at the moment, but photons seem to have no mass at rest and some mass while moving. Electrons, in this case as beta radiation, and alpha radiation, a collection of protons and neutrons, are all a bit heavier and more highly charged. They’re all very tiny from our perspective, but collections of protons and neutrons are a bit heavier than electrons which are a bit heavier than photons. The charged electrons and alpha particles, protons and neutrons together, can be deflected or controlled by a magnetic field. This can help us see the shape of the Sun’s magnetic field in its corona. Just like a magnet on a bed of iron filings, we can see lines coming out of the poles and curving around the Sun to form a loop, connecting the North and South Pole. The material around the Sun constrained by this field help to highlight it, and it’s the reason the corona of the Sun looks the way it does.

The Earth’s magnetic field works the same way, stretching out from the poles and wrapping around the planet. The magnetic North and South Poles aren’t exactly the same as the geophysical poles, but they are pretty close. Just like the Sun, and all magnets, we have lines of magnetism, our magnetic field, flowing from the North Pole to the South Pole, around the sides of the Earth. These lines are high above the equator nd temperate regions of the planet, but at the poles these lines of the magnetic field funnel back down. The magnetic field passes through the center of the Earth, as the Sun’s does through the Sun. This brings the magnetic field through our atmosphere in the far North and South. When particles from the Sun crash into the Earth, they hit our surrounding magnetic field first. Photons are usually able to get straight through, our magnetic field isn’t going to push on photons that much, though some energy is blocked or absorbed in the upper atmosphere. Electrons and other heavy, charged particles however, they do get pushed around by our magnetic field. Even when material from the Sun is crashing into the Earth’s magnetosphere above the the equator, the magnetic field of the Earth catches those high-energy particles and guides them to the North and to the South Pole. This is where the high energy particles have a chance to interact with our atmosphere. As I mention in the video, I can’t seem to simulate aurorae in Stellarium, so if any one knows a way to do it or a plug-in I can download for it, do let me know.

The aurorae are beautiful lights in the sky, comparable in impressiveness to the Milky Way. The Milky Way however is static, it sits there in the sky. Aurorae will dance and flow around as they are streams of particles, crashing into the Earth’s atmosphere. As high-energy particles collide with our upper atmosphere they generate light, the high-energy particles pass on some of their energy to gases in our atmosphere like oxygen and nitrogen, causing them to light up. As particles flow along and down our magnetic field, and as the field itself wobbles and shifts, the patterns and colours of the aurorae change, making it particularly impressive to see. This same process happens on other planets with magnetic fields and atmospheres. Saturn has aurorae around the North and South Pole, as does Jupiter. Jupiter’s aurorae can be particularly big due to the size of the planet and its strong magnetic field. Even on these other planets, the shape of the magnetic field brings particles down to the atmosphere at the Poles. This is why we see aurorae at the North and South Pole, they are the Aurora Australis and Aurora Borealis, not the Aurora Equatorialis, which would be around equator,

This happens all the time, the Sun is always sending high energy particles our way, so close to the magnetic poles aurorae are pretty common. When we have very powerful storms, the amount of material crashing into the magnetic field increases and how close to the equator those high energy particles are guided into the Earth’s atmosphere increases as well. Weaker storms are reasonably common, allowing aurorae to be seen regularly inside the Arctic Circle. Only more powerful storms can cause aurorae closer to the equator, and these more powerful storms are rarer. Larger storms most commonly occur close to the peak of the solar maximum when there is more solar activity in general. We are not up to the peak of our current solar cycle just yet, and we’ve already had a storm causing aurorae which have been visible as far South us here in Ireland. They also seem to have been visible even further South, in mainland Europe, even in Germany, Poland and parts of Spain. Normally, only countries closer to the Arctic Circle, such as Iceland or the top of Norway, Finland or Sweden, have a chance to see them. The storm which just occurred was certainly strong, but stronger storms have happened in the past, with aurorae visible right down into the Mediterranean at least.

Most of the more powerful storms happened during cycles with higher peaks. Although the Sun goes through a regular 11-year cycle of high and low activity, some cycles have higher peaks than others. Usually, a few higher peaks will come together, such as the modern maximum in the 1950’s. A few years of higher activity like this is usually followed by a few years of lower peaks, such as the Maunder Minimum a few hundred years ago. There can be periods of time where the Sun has barely any sunspots even at its maximums. Since the higher peaks in the 1950s, we’ve had reasonably low peaks for a few solar cycles. Since the beginning of this solar cycle, there has been more sunspots and solar storms, earlier in the cycle, than the past few. This indicates that the peak, which as I’ve said is yet to come, will be comparatively higher as well. This means that even if you didn’t get to see the most recent aurora, there is a good chance that we will have some other chances to see them even at low latitudes over the next few years. This isn’t guaranteed of course, the solar storms can go in any direction and may miss the Earth entirely even if they are strong. We might also get a more powerful storm, sunspots and solar storms are hard to predict in the long term, but it also takes a while for a solar storm to hit the Earth after leaving the Sun. This means that in the short term, aurorae are quite predictable, we can have a fair idea of when they will be good a day or so in advance, but not weeks or months. There are plenty of services out there that will tell you when aurorae are coming up when solar storms occur, but it is hard to predict them far enough in the future to prepare people further in advance. Then again, there’s not much to do to see the aurorae, except being far enough North during a powerful enough solar storm. Of course it helps if you’re in the countryside and if you have a clear sky.

Not the shortest possible explanation, but I hope you found it to be a good one. I will keep hoping for a bigger solar storm over the next couple of years, and I may make a video about the maximum and minimum when we reach them. If you’d like to catch those posts, you can subscribe to this website, my YouTube channel, or both. Whether you do or don’t, I hope you’ll come back for the next one.