April 27, 2004
The photos above were taken near Brittany, France in late February. It was a fresh day (about 5° C or 42 F), and the sky was clear except for a thin layer of altostratus clouds. I happened to notice the irisations at the border of these clouds about half an hour before I took the first picture. On this one minute or so sequence, one can readily see the changes in color and shape that occurred in the clouds. Irisation or iridescence can be thought of as detached coronae and are caused by diffraction of sunlight -- minute water droplets in clouds interfere with sunlight.
Photo details: Kodak DC3400 digital camera, 1/700 exposure, focal length of 76 mm.