An aurora happens when energetic electrically charged particles, like electrons, collide with atoms

Anaurora happens when energetic electrically charged particles, like electrons, collide with atoms of gas as they accelerate along the Earth’s magnetic field lines in the upper atmosphere.

Those collisions cause the atoms to give off light. Auroras are a lot like neon signs, except that the conducting gas is in the Earth’s ionosphere instead of inside a glass tube.