How to

13 June 2016

The Science Behind the Northern Lights

For many tourists who choose to venture to the northernmost parts of Canada, Alaska, Scandinavia or further still, the northern lights are the biggest draw. The aurora borealis, and their southern counterpart, the aurora australis, are amazing, vibrant displays of colour which can only be seen in the most northerly and southerly parts of the world. They have fuelled mythology, astounded explorers and fascinated scientists for centuries, but what exactly are they?

In order to understand why auroras happen, you have to look at the sun. It can be easy to forget sometimes that, far from simply being a ball of light and warmth in the distance, the sun is a ball of incomprehensively potent thermonuclear energy. Now and again, storms will rage, but not the kind we’re familiar with down here on terra firma. Solar winds are streams of heavily charged particles which whip across the sun’s surface and in the most extreme cases actually break out of its sizeable gravitational pull.

When this happens, they can actually reach Earth’s atmosphere, in what is known as a geomagnetic storm. This has a number of different knock-on effects, including radiation increases, malfunctions in navigation equipment or even the overload of electrical transformers. When these supercharged solar protons and electrons collide with our own home-grown atoms and molecules, they become excited.

That might sound like an abstract term, but it’s an accurate one. As atoms become excited, their electrons move further from the nucleus, then when they calm and draw back in, they release photon particles. Photons produce light, and depending on the force and direction of the magnetic disruptions, this can result in auroras.
Typically they’re green, but when the effect is stronger they might be red, violet or pink, it also depends on which atmospheric gas is being affected the most and at what altitude. If it’s oxygen, and up to 150 miles in altitude, it’ll be green, but if it’s above 150 it’ll be red. Nitrogen shows up blue up to 60 miles, and turns purple above that.

Sometimes they appear as a faint, distant glow, other times as wavering arcs and sometimes as spirals. The movements are a result of the constantly shifting molecular combinations, brimming with an electrical charge in excess of 20,000,000 amperes, at 50,000 volts.

The reason you only tend to see them in the coldest parts of the world, near the poles, is because they sit beneath the most strongly magnetically charged parts of the planet’s atmosphere. This can change though, depending on sunspot activity.

If you look at close up images of the sun, you can sometimes see dark blemishes on the surface. These are sunspots, disruptions in the magnetic field which cause a drop in surface temperature. Most of the time there are too few of them to have any kind of prominent effect on us, but they move in 11 year cycles, and when they’re at their most concentrated, more particles escape the solar gravitational field than usual, resulting in a far wider spread of auroras. 

Callum Davies

Callum is a film school graduate who is now making a name for himself as a journalist and content writer. His vices include flat whites and 90s hip-hop.