Northern Lights colors, explained simply. Aurora color depends on two things: What gas the sun hits. How high it happens above Earth. Green is the most common. It happens when solar energy hits oxygen lower in the atmosphere, roughly 60–120 miles high. There is more air at this level, which is why green aurora shows up so often. Purple usually means movement. It forms when solar energy hits nitrogen and often appears along the edges of green aurora or during fast, active nights. Red is rare. Red