This Christmas break, I travelled to Reykjavik, Iceland for a mini-break. Winter days in the North are short, which meant we had three long nights to hunt down the Northern Lights – a sight I’d never seen before and was very eager to see. After two failed evenings in which a blizzard, clouds, and city lights threw some spanners in the works, I must admit I was giving up hope. But after a while, we spotted a patch of slightly brighter sky. It became steadily greener and brighter, and then there was no doubt about it: we were witnessing one of the most beautiful spectacles to be found in nature.
Looking up at the bright green lights dancing away on the horizon, I could understand that traditional people’s devised mythological explanations for this strange phenomenon, such as it being a bridge to heaven. Especially as I couldn’t remember how it worked myself, whilst admiring the sight, I felt a niggling of curiosity at the back of my mind. What are these lights and how do they work?
The Northern and Southern Lights, Aurora Borealis and Australis, are a product of an interaction between the Sun and the Earth. Solar winds continually release particles into the universe. The Earth’s magnetosphere – a giant magnetic force field – protects us from most of these particles. But the solar winds also set in motion electrons that are already in the magnetosphere, which manage to make their way into our atmosphere. When they bump into oxygen and nitrogen molecules in the sky, the energy from the electrons is transferred, putting the atmospheric particles in an ‘excited’ state. When oxygen and nitrogen return to their normal state, they release excess energy in the form of photons: the light that makes up the Aurorae.
Most often, the lights are bright green, but they can come in a spectacular range of colours. The colour differences stem from a difference in particle type, electron energy, and collision height: oxygen gives off green light, nitrogen emits blue light, and low energy electrons show red light. Not only do they mix to form brilliant colour displays/combinations, the Northern Lights also seem to ‘dance’. That effect is due to the Earth’s magnetic fields interacting with the electric currents created by the moving electrons.
Those magnetic fields are precisely the reason that we have to travel to the desolate icy plains in the North to see the Lights. The electrons causing the Aurorae don’t just randomly collide with the atmosphere – they are guided along the Earth’s magnetic field lines in such a way that they only hit the sky around the ‘auroral ovals’. In the North, this means you can see them in northern Scandinavia, Russia, Alaska, Canada and Greenland. Only when solar activity is very intense do the auroral ovals widen enough to see the Aurora Australis in southern Australia, New Zealand and Chile – normally the sight is lost to the human eye as it’s only visible over the Antarctic seas.
It’s only since space exploration took off in the 1960’s that scientific theories about the Aurorae can be tested, and we still don’t know everything about them. The Northern Lights display I saw looked like giant arcs on the horizon, but they come in all shapes and sizes – how that works is still a mystery. The curl shape they sometimes take is subject of a current NASA-funded mission: on 24 January 2014, scientists launched a sounding rocket straight into the Aurora. The aim of this investigation is to find out more about the transfer of energy from the Sun. For the researchers, the Northern Lights are merely a side effect of this energy transfer, but to me they were the highlight of my Iceland trip. If you missed the UK display this month, I’d wholeheartedly recommend an Auroral expedition to witness this most breathtaking of natural phenomena.