Insane Northern Lights from last night over Stonehenge. Aurora colors appear at different heights in Earth’s upper atmosphere.Green light is most common and forms lowest, typically around 90 to 150 km above the ground, produced by oxygen atoms. Red auroras occur much higher, about 200 to 400 km, also from oxygen but in thinner air where energy lasts longer. Purple and violet tones appear lower than green, roughly 80 to 100 km, caused by excited nitrogen. Blue hues form at the very lowest visib