#PPOD: Due to airglow, which is usually hard to see, the sky can glow like a giant rainbow. Disturbances like storms cause gravity waves, making airglow visible. The colors likely originate from various molecules: deep red from OH molecules at 87 km high, and orange and green from sodium and oxygen atoms higher up. This image was captured on Mount Pico in the Azores, Portugal, with Faial Island's lights in view. Credit: Miguel Claro | Dark Sky® Alqueva
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