Explanation: Colourful star trails arc through the night in this wide-angle mountain and skyscape. From a rotating planet, the digitally added consecutive exposures were made with a camera fixed to a tripod and looking south, over northern Iran's Alborz Mountain range. The stars trace concentric arcs around the planet's south celestial pole, below the scene's rugged horizon. Combined, the many short exposures also bring out the pretty star colours. Bluish trails are from stars hotter than our Sun, while yellowish trails are from cooler stars. Near the center, the remarkably pinkish trail was traced by the star-forming Orion Nebula.

Explanation: Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water. Red airglow likely originates from OH molecules about 87-kilometers high, excited by ultraviolet light from the Sun, while orange and green airglow is likely caused by sodium and oxygen atoms slightly higher up. While driving near Keluke Lake in Qinghai Provence in China, the photographer originally noticed mainly the impressive central band of the Milky Way Galaxy. Stopping to photograph it, surprisingly, the resulting sensitive camera image showed airglow bands to be quite prominent and span the entire sky. The featured image has been digitally enhanced to make the colors more vibran