Encore - Mock Green Flash from Sunset Cliffs, California

January 16, 2016


Today, and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.

Photographer: Jim Grant
Summary Author: Jim Grant; Jim Foster

The photo above showing a mock green flash was taken at sunset from Sunset Cliffs, California. A thermal inversion (relatively cool air overlain by warmer air) was set up over the coastal Pacific Ocean, which greatly distorted the Sun's shape and permitted this green flash to be more easily observed. When the Sun is near or on the horizon, refraction in the lower atmosphere in effect squashes the solar disk so that rays of sunlight from the bottom of the Sun pass through a denser atmosphere than rays coming from the top of the Sun. As a result, the bottom portion of the Sun is refracted more noticeably than is the top portion. Shorter wavelength green light is refracted more than red light (longer wavelength). Thus, we see a very slight separation between the red and green images of the setting or rising Sun -- a green upper edge and a red lower one. This effect is best seen using binoculars. However, if a mirage is present, as was the case on this day, the Sun's disk is distorted (magnified) and the green coloration is more easily differentiated. Always protect your eyes when looking toward the Sun, even when it lies on the horizon. Photo taken on December 13, 2010.

Photo Details: Camera Maker: NIKON CORPORATION; Camera Model: NIKON D80; Focal Length: 210mm (35mm equivalent: 315mm); Aperture: f/5.6; Exposure Time: 0.0013 s (1/800); ISO equiv: 200; Exposure Bias: none; Metering Mode: Matrix; White Balance: Auto; Flash Fired: No; Color Space: sRGB.