The Northern Lights appear in different colours depending on the gases with which the solar particles collide. Generally they appear in colours of green, yellow, blue, purple, pink, and red. The most common colour is green, due to the impact of solar particles with oxygen atoms. Blue, purple, and pink are rarer to see and are associated with solar particles colliding with nitrogen atoms. Red is the rarest colour to see and is associated with solar particles hitting oxygen atoms but at a higher altitude above 150 miles.