The mysterious green flash

Jules Verne's 1882 novel Le Rayon vert (The Green Ray) focused on a rarely seen optical phenomenon. In the last moment of sunset at sea, the remaining glimmer of sun may turn “a green which no artist could ever obtain on his palette … If there is a green in Paradise, it cannot be but of this shade”. Skeptics long thought the green flash might have been a visual after-image produced by staring at the setting sun, but it can also occur at sunrise. Others considered it a result of sunlight passing through waves on the water, yet it's also been reported over the desert. The flash can be explained by thinking of the atmosphere as a prism that separates the disk of the setting Sun into a rainbow spectrum: violet on top, red on the bottom. Violet would normally be the last visible colour, but since the atmosphere tends to scatter blue and violet light out of the direct beam, what's left in it is green. Photographers struggle with the green flash's brevity (a second or less in most places) and its tiny dimensions (too small for anything but enormous telephoto lenses to capture). At high latitudes, the Sun can hover just at, or below, the horizon for hours in the summer, making for a prolonged show of greenery. On October 16,1929, an Antarctic exploration team led by Richard Byrd watched the green flash come and go over a 35-minute span.