What causes the colours of the aurora?

 
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A magical fox, running across the Arctic fells, its tail spraying snow and sparks into the air. The dead, playing football in the heavens with a walrus skull. Or the souls of dead children, dancing in the sky.

These are myths surrounding the aurora, stories ancient cultures close to the North Pole told to explain the ethereal lights they saw flickering in the night sky above their heads. Now, we know that these breathtaking displays aren’t of supernatural origin but due to chemical processes high in the atmosphere. This graphic explains how auroras form and what causes the different colours.
 
While the aurora may not be paranormal, their origins are extraterrestrial. Their genesis is in charged particles ejected from the sun’s surface, a stream known as the solar wind. These particles, mostly electrons and protons, are flung from the sun’s corona at speeds of around three hundred kilometres per second and hurtle through the whole solar system.

When these particles reach Earth, our planet’s magnetic field shields us from them. This is a good thing because, without this shielding, the charged particles would wreak havoc with our electronic and communications devices and networks. Earth’s magnetic field shield deflects the majority of the solar wind around the planet; however, a small number of particles enter the atmosphere at the magnetic field’s weak point, the poles.

Once the charged particles, primarily electrons, have entered the atmosphere, the atoms and molecules in their path are at their mercy. High-speed collisions transfer extra energy to air atoms and molecules, a process called excitation. These excited atoms and molecules don’t remain in this state for long; they return to their original or ground state, losing their excess energy as light. This process generates the aurora. 

This article was originally published by Compound Interest. For read the full version of this article, please visit Compound Interest/Aurora.