Glory, Spectre and Fog Bow on Reunion Island

July 12, 2011

Glory-day 
Photographer: Luc Perrot; Luc's Website
Summary Author: Luc Perrot; Jim Foster

July 2011 Earth Science Picture of the Day Viewer's Choice; Best of 2011

The image above featuring a fine example of a fogbow arching over a Brocken spectre and glory was taken on Reunion Island using time-lapse photography. I placed my camera on a tripod, which allowed me to raise my arms during the shooting. The Brocken spectre and glory result primarily from diffraction -- deflection of sunlight about minute cloud droplets. They only form at the antisolar point. Since shadows converge at the antisolar point, the shadow of the photographer or that of the aircraft you're flying in will usually be observed. If the shadow appears ghost-like, because of distortion, it's referred to as a Brocken spectre.

Fogbows form in a way similar to rainbows -- sunlight is refracted and redirected inside of water droplets. However, because the cloud droplets are much smaller than raindrops, the geometric optics are much different. Diffraction of sunlight, not refraction, is much more important. Fogbows are largely pale in color because the very small droplets ensure that colors overlap.

You can also view this phenomenon on a time-lapse video. Photo taken on June 10, 2011.