The air glows all the time, but it’s often hard to see. However, a disturbance -- such as an approaching storm -- can cause noticeable ripples in Earth’s atmosphere. These gravitational waves are oscillations in the air analogous to those created when a stone is thrown into calm water. Long-term exposure, almost along the vertical walls of the airglow, probably made the rippled structure particularly visible. OK, but where do the colors come from? The deep red glow probably originates from OH molecules about 87 kilometers up, excited by ultraviolet light from the Sun. The featured image was captured during a climb to Mount Pico in the Azores, Portugal. Earthly lights originate from the island of Faial in the Atlantic Ocean. A spectacular sky is visible through this banded atmospheric glow, with the central band of our Milky Way running up the center of the image, and M31, the Andromeda Galaxy, visible near the upper left.