August 7, 2013
This extraordinary sighting has been experienced in the daylight sky, since the beginning of man. Iridescent colours in clouds are given many other names including Fire Rainbows.
Simply they are formed when tiny water droplets collide with ice crystals and scatter the light – a photographer’s dream palette.
The phenomenon is often referred to as cloud iridescence or irisation. The term comes from Iris, the Greek personification of the rainbow. And there is the physics behind: see some of our links below.
For those in the Southern Hemisphere, we are coming up into the best period for seeing these with our clear winter skies and coldness remaining in most areas. Here in Australia it does occur more frequently in Spring and Autumn. Lucky us!
To see them, the sun must be very high in the sky, preferably at least 58° or greater and there must be high altitude of cirrus clouds (preferably coming off the cold). Circumhorizontal arcs are different to Iridescent clouds, no matter which one you see these are very remarkable.
Interesting Facebook Groups
Earth Sky
Interesting Web Sites
Cloud Appreciation Society
They even have an iphone app for cloud spotting!
http://cloudspotterapp.com
Amusing Planet
Atmospheric Optics
