The green hue of the northern lights is not caused by refraction. It’s caused by oxygen molecules giving off light after interacting with charged particles from

The green hue of the northern lights is not caused by refraction. It’s caused by oxygen molecules giving off light after interacting with charged particles from the solar wind (which is being directed by the earths magnetic field into the atmosphere at northern latitudes.) Oxygen gives off photons in a greenish hue when the excited electrons return to their ground state, while nitrogen gives off a bluer hue, etc.