Cloud iridescence, also known as irisation, occurs when tiny water droplets or ice crystals in clouds scatter light in a particular way. These clouds display bright, rainbow-like colors similar to those seen in soap bubbles or oil slicks.
The phenomenon typically occurs in:
- Thin clouds close to the sun
- Altocumulus, cirrocumulus, or lenticular clouds
- Clouds containing water droplets of similar size
The colors appear when sunlight is diffracted by uniformly-sized cloud droplets. The effect is most visible when clouds are thin and the sun is partially obscured. For safety, observers should never look directly at the sun while seeking these colorful displays. The most vibrant iridescent clouds often appear within 10-20 degrees of the sun.