What causes the Northern Lights to vary in colour?

The colours of the Northern Lights, or aurora borealis, depend on the types of gases in Earth’s atmosphere and their altitude. Oxygen at higher altitudes (above 150 miles) emits red and green light, while oxygen at lower altitudes (around 60 miles) produces green light. Nitrogen, which is abundant in the atmosphere, can create purples, blues, and pinks when it interacts with charged particles. The intensity and variety of colours also depend on the solar activity that triggers the aurora.