Switch on the Northern Lights, please!

Not long ago I had the chance to travel to what is considered the most northern city in the world, Tromsø, in Norway. The reason was clear, I wanted to see one of the most amazing natural events, namely the Northern Lights. In this respect, this post tries to gather all my experience, the science behind this phenomenon and some basic advice if you want to go there.

‘Northern Lights’ is the common term for an event scientifically known as ‘Aurora borealis’, which occurs in the north pole. An analogous phenomenon takes place in the south pole, known in this case as the ‘Southern Lights’, or technically ‘Aurora australis’. So, does this spectacular phenomenon only take place in the poles? Unfortunately, the answer to this question is ‘Yes’, let me try to explain why.

Sun storms.

First of all, let’s talk about the Sun, as it’s where our story begins. It’s commonly known that the Sun is a star, which means in the end that it is a huge nuclear fusion reactor. The Sun’s core contains large amounts of hydrogen, which are confined within an extremely high pressure and temperature. This high pressure, together with this high temperature, causes that when two hydrogen atoms collide, they do not bounce, but they join together. These two joined hydrogen atoms no longer have hydrogen properties, they have different ones, and thus we call this product helium. A nuclear fusion reaction has occurred. This nuclear reaction produces a lot of energy, which heats its environment and tends to rise the pressure and the temperature. But what does this imply? This reaction has a physical consequence: it makes the particles to have a very high vibration (i.e. temperature), and thus to separate from each other, producing the state known as plasma. When in a plasma state, the particles (electrons, protons, heavy nuclei, etc.) are completely free, and thus producing a flow inside the star. So what do charged particles in motion produce? Exactly, a magnetic field. Avoiding the more technical aspects, relatively recent research (here) has proved a relationship between Coronal Mass Ejections (CME) and the Sun’s magnetic field. Therefore, we’re gotten to the point, a deviation in this magnetic field, caused by the inner nuclear reactions in the Sun, eventually produces a huge mass of particles to be pushed away to the outer space. This ejected material (in the form of a CME, solar wind, etc.) is a plasma, compounded basically by protons and electrons, but may contain small quantities of helium or heavier elements.

In fact, these ejections might turn into nothing, they might get lost in the outer space. But what if one of these is thrown towards the Earth? It typically takes these particles one to five days to reach the Earth, and while getting closer, they start to feel something familiar, a magnetic field, now the Earth one.

Structure of the Earth’s magnetosphere.

As this gust approaches to the Earth, it starts to feel the magnetic forces and so its trajectory is bent, towards where? Towards the magnetic poles, which are more or less the same as geographic poles (let’s avoid topographic discussions at this point). The bigger the ejection, the more ‘resistant’ its flow will be, and therefore we will be able to see the lights further away from the poles. When this particles reach the upper atmosphere, they have a very high speed (from 20 km/s to 3200 km/s, 489 km/s on average), which means that they have a lot of energy. As they slow down due to the atmosphere density, they lose energy, and this energy is lost in the form of photons, i.e. light!

Aurora borealis from the space.

So, what’s important about this science behind? The Northern Lights cannot be predicted with certainty. You can only do your best to see them, though. What matters, then? First of all, you need solar activity. This issue is fairly well monitored by several international organisations. The website I used is this website by the Geophysical Institute (University of Alaska), which establishes a quantitative indicator for aurora activity in a nine-point scale, particularized for every zone of the planet. What more? The sky must be clear. This phenomenon occurs in the upper parts of the atmosphere, just on the clouds; if the sky is cloudy, you won’t see anything. Regarding this second point, I do recommend you to follow an organised trip. Most of them keep in touch and tell each other where the best places are in a particular day. If you go to the North of Norway, you can be in the surroundings of Tromsø, far to the North or far to the south, it’s the weather in each of these places that will make the difference. And last but not least, you must go to a place without light pollution, as it won’t let you see anything. This point is also taken into account by professional tour operators. Once you have been there for a while, you’ll realise how important the location is.

As far as my experience is concerned, I went two times, in mid-March, to ‘chase’ (as they call it) the Northern Lights with two different tour operators, and I was lucky the second time. In the first time, we encountered a completely clear sky, but there was not any solar activity whatsoever (I think it’s completely unfair to say the name of the tour operator, so I won’t). This is an extremely rare situation, so you won’t probably be in one of these; if you see a clear sky, you’ll probably see the lights. The second time, I went with Tromsø Friluftsenter and the sky was almost completely clear. The aurora in the picture below is the one I saw.

The Aurora borealis I saw!

I have to admit that I expected more. It has to be said, though, that the one I saw was a 3 (in the former nine-point scale) and it was like a green cloud in the sky. Now, from my past experience, I think that the key to really enjoy this phenomenon is to own a very good reflex camera, which was not my case, because these cameras will let you capture pictures like the one on the left. Nevertheless, overall it’s definitely an experience I recommend. Maybe you are more lucky than I was, and you can see a 9-point aurora!

Anyway, be patient. Spend as much time as you have watching the sky, perhaps it’s not what you had expected, but surely you won’t get disappointed!