Green airglow and gravity wave clouds in the night sky over Canyonlands National Park, Utah, USA. Airglow is a phenomenon where a planetary atmosphere emits a faint glow when atoms are excited by sunlight. The banding of the glow here is caused by gravity waves in the atmosphere, where weather systems generate large waves as buoyant air masses rise and sink due to the effects of gravity, often as a flow of air meets mountains.