Iridescent wave-clouds (w-399-21)
In gallery: Photos of the month (2002)
Related photos: Atmospheric optics
Wave-clouds usually are transient clouds. When they are just forming, they consist of small cloud droplets which are almost uniform in size. These droplets can diffract sunlight, giving the cloud colors like those seen also in soap bubbles, and oil-films on water.
Photo taken in Holland, early March 2002.