An aurora is an atmospheric effect produced when charged particles from the radiation belts surrounding a planet like the Earth, are accelerated down the magnetic field lines near the north and south magnetic poles. They collide with atoms of gas in the atmosphere such as nitrogen and oxygen, and the collisions cause the atoms to emit light at very specific wavelengths. This causes aurora to have red and blue colors. All of this happens between 70 and 300 kilometers above the ground and requires very low gas densities.