Iridescence Over Canyonlands National Park
June 17, 2013
Photographer: Alissa Pajer
Summary Authors: Alissa Pajer; Jim Foster
The photo above shows a lovely example of iridescent clouds, as observed from Canyonlands National Park, Utah. The rock formation at lower center was used to block out direct sunlight. Sunlight deflecting off similar-sized cloud droplets, typically in mid-level clouds, results in the metallic colors. The droplets are of just the right size (approximately 20 or so micrometers across and many times smaller than raindrops) to interfere with wavelengths of visible light. Very small differences in the shape and size of the droplets cause differences in brightness intensity. An iridescent cloud is essentially a detached corona and thus most of the time appears in the vicinity of the Sun. Always use utmost care when looking at iridescent clouds. Photo taken on January 5, 2012.
Photo details: Photo created by combining two exposures; one with f/13 and 1/4000 sec. exposure, the other with f/5 and 1/2000 sec. exposure.