Circumhorizontal arc - HD 影片檔

Timelapse footage of a circumhorizontal arc seen in high-altitude cirrocumulus clouds. The spectral colours of the arc are produced by the refraction of sunlight through flat hexagonal ice crystals in high cloud. The arc appears at a distance of 46 degrees from the Sun. Due to the geometries required by the ice crystals and light paths, the arc can only be seen when the Sun is high in the air, at least 58 degrees above the horizon. Filmed in the USA at midday in summer.