Flattened Sun and Green Flash
May 21, 2004
The photo above showing a distorted but colorful setting Sun was taken in Finland by Pekka Parviainen. The "Green Flash" is an actual phenomenon and not a camera artifact. While it's not often observed, this colorful flash occurs to some degree each time the Sun sets or rises -- it can also look blue-green or even bluish. Dispersion in the atmosphere smears the setting Sun in such a way that a separate "image" appears for the red color, yellow color and the green color as well. As shown above, the rims of these "images" are stacked with the green rim on top and the red most on the bottom.
The distortion in the shape of the Sun itself is a consequence of atmospheric refraction by the curved atmosphere, which acts as a lens and "pushes up" objects that are near the horizon. The closer to the horizon, the greater the effect, and so the lower portion of the Sun is pushed upwards more than the upper portion, causing the disk to appear squashed or flattened.