The aurora is comprised of 3 main colours: Green, Red, and Blue
Light
When we see colour it is because the light going in our eye has a particular wavelength (This is just the measure of how far a wave travels before it does one cycle).
White light is the combination of lots of different colours. Which means a combination of lots of different wavelengths. This is why when we put a prism in front of the light it splits it into a rainbow.
Each colour has its own range of wavelengths:
- Red - 700-620 nanometres (this is the wavelength)
- Orange - 620-597 nm (nm=nanometres)
- Yellow - 597 - 577 nm
- Green - 577-492 nm
- Blue - 492-455 nm
- Violet - 455 - 400 nm
Anything below 400 nanometres is considered ultraviolet. Anything above 700 nm is called infra-red. Everybody sees colours differently, so these are really just guidelines.
Aurora light
Each colour in the aurora is a result of different elements going through some kind of energy process, where at the end they emit light. Because of how quantum physics works we can actually predict what these colours are; quite accurately as well.
Red
Red light is created when an oxygen element in the atmosphere is hit by an electron. This causes it to gain energy. To lose this energy the oxygen emits a photon (light) with a wavelength of exactly 630 nm. Which is red!
Green
Green is almost the exact same process as the red. An electron comes in and hits the oxygen giving it some energy. Only this time, the electron has a little more energy; meaning the oxygen has more energy to get rid of. To solve this problem the oxygen releases light with a shorter wavelength of 557.7nm
Because the electron has more energy it can make it further down the atmosphere which is why we often see green aurora at the bottom.
Is the result of what is called ionised molecular nitrogen. We consider the same process as the other two, but instead of an oxygen we have two nitrogens stuck together. When the electron hits the molecular nitrogen goes up in energy. To lose the energy the molecule emits a photon with a wavelength of 428nm.
This is often referred to as blue aurora, but can appear purple or pink as well.
Next: Why knowing the colours is cool
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