miércoles, 24 de abril de 2013

I saw a cloud with rainbow colors. What causes it?

Iridescent clouds – clouds with rainbow colors – happen when small water droplets or small ice crystals individually sctter light.

Sky watchers on occasion report seeing colors in the clouds, and sometimes our friends send photos of these rainbow-like clouds. You’ll find some examples below. These colorful clouds are called iridescent clouds, and the phenomenon is called cloud iridescence or irisation. The term comes from Iris, the Greek personification of the rainbow. When you see a cloud like this, you know there are ice crystals or small water droplets in the air. Larger ice crystals produce solar or lunar halos, but tiny ice crystals or water droplets cause light to be diffracted – spread out – creating this rainbow-like effect in the clouds. See the images below, mostly via EarthSky friends on Facebook and Google+, for more about iridescent clouds.

Iridescent cloud seen by EarthSky G+ friend Dave Walker on April 17, 2013. View larger. He wrote, “Through gaps in the fast moving lower clouds I spotted these beautifully coloured high clouds as the sun headed for the horizon. Added a little vibrance and contrast enhancement but otherwise the colors here are as I saw them.”

The best way to see an iridescent cloud is to place the sun itself behind some foreground object, a building or mountain, for example. Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water. EarthSky Facebook friend Duke Marsh captured this image on September 9, 2012 in New Albany, Indiana.

Rosanne Harter Haaland in Johnson City, Tennessee captured this beautiful iridescent cloud on January 24, 2013..

source and credit a earthsky