Wave Cloud Iridescence    Imaged in New Zealand by Tony Travaglia. These clouds were only 5° from the sun.  Clouds produced by vertical wave motion are perfect candidates for iridescence. Air forced upwards by the wave expands and cools. Moisture condenses into small droplets.  Then, sometimes within a few seconds, the droplet laden air is forced down again. It is compressed and heated - the droplets evaporate. The droplets all have short lives and the same history, consequently they are small and of very similar sizes - ideal for bright iridescence. Image ©Tony Travaglia , shown with permission.