Aurora Over Clouds
Aurorae usually occur high above the clouds. The auroral glow is created when fast-moving charged particles from the Earth's magnetosphere impact air molecules high in the Earth's atmosphere . An oxygen molecule , for example, will emit a green light when reacquiring an electron lost during a collision. The lowest part of an aurora will typically occur at 100 kilometers and up, while most clouds usually exist only below about 10 kilometers. The relative heights of cloud s and auroras are shown clearly in the above picture taken last month from near Quebec City, Canada . The most likely time to see an aurora is around midnight.