Green Glow Down Low
August 30, 2011
It’s a green flash as observed from Paris, France at sunrise on July 17, 2011. The green flash is a refraction phenomenon caused by dispersion in the atmosphere, which allows separate “images” of the Sun to be discerned in red, yellow and green. The rims of these images are stacked with the green rim on top and the red on the bottom. When conditions permit, the uppermost rim will emerge (for the case of sunrise) with a flash of green color. Flashes are much easier to see over water than over land. They’re also easier to view at sunset than at sunrise since you have to know exactly where the Sun will break the horizon in order to catch the burst of color. Click here for a view of the green flash a few seconds later. Note that the crimson streak is a mid- or high-altitude cloud. It’s reddened by the increased path length of sunlight that results when the Sun is on or below the horizon. Always be very careful anytime you’re looking toward the Sun.
Photo details: Canon EOS 7D camera; Orion 80ED telescope; 1/8000 sec. exposure; 100 ISO.