Iridescence and Corona
February 20, 2013
Photographer: Fausto Lubatti
Summary Authors: Fausto Lubatti; Jim Foster
While snowshoeing with friends on a beautiful winter's afternoon in the Val Biandino of northern Italy, I couldn't help but notice the striking iridescent clouds shown above. The slope of the valley effectively blocked the Sun, accentuating the iridescence or opalescence. Additionally, a colorful corona surrounding the Sun was easily visible. Cloud iridescence and coronas are both caused by diffraction processes. The mid-level clouds on the left side of the photo are formed by very fine droplets of similar sizes. These droplets deflect sunlight -- they interfere with light in such a way to produce patterns of colored rings. Note that the cumulus clouds at right (lower altitude) are composed of droplets of generally larger sizes and show no iridescence. Be sure to protect your eyes anytime you look in the vicinity of the Sun. Photo taken on January 5, 2013.
Photo details: Camera Model: Canon EOS 5D Mark II; Lens: EF35mm f/2; Focal Length: 35.0mm; Aperture: f/13.0; Exposure Time: 0.0025 s (1/400); ISO equiv: 100; Software: GIMP 2.6.11.