Iridesence in Clouds Over Gran Paradiso National Park, Italy
May 26, 2011
The photo above showing irisation (iridescence) in cumulus clouds was taken over the sharp summits of Gran Paradiso National Park, Italy. The pastel-like colors result from diffraction of sunlight in cloud droplets having similar sizes. With diffraction, light is deflected around the outside of the tiny droplets rather than through them, as is the case with refraction (solar halos and arcs are caused by refraction of sunlight). Colors are more remarkable about cloud edges since the droplets are quite uniform here and the angle of diffraction is more or less fixed. Note that the colorful "arc" at upper left is a lens artifact. Photo taken on December 28, 2008 at about 12:30 p.m.
Photo details: Camera Maker: Canon; Camera Model: Canon EOS 30D; Focal Length: 75mm; Aperture: f/9.0; Exposure Time: 0.0001 s (1/8000); ISO equiv: 200; Exposure Bias: none; Metering Mode: Spot; Exposure Mode: Manual; White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB. Photoshop used to enhance colors.