For a few days every spring and every fall, the sun sets between the towers of the Golden Gate Bridge. When the air is clear and the turbulence level is low, and the layers of atmospheric refraction are just right, the rare "green flash" is visible for a fraction of a second just as the disk of the sun sinks behind the horizon.

The photo is a single frame extracted from a short video clip. The camera is a Canon S2IS, hand-held at 12:1 zoom.
