GRAND RAPIDS, Mich. (WOOD) — Beautiful clouds with splashes of rainbow colors were spotted across West Michigan skies on Thursday. The effect is called iridescence and it happens when very small water droplets scatter light in a special sort of way.
This effect is only spotted when cloud droplets are especially small and very uniform in size. Often when a cloud is newly formed, or “young,” and the water droplets are all similar in size. This is why the phenomenon is most common in new clouds.
Although a rare phenomenon, iridescence is seen mostly in thin clouds. The term iridescence comes from the Greek goddess of rainbows, Iris.
The brilliance of iridescence in a cloud can change depending on where you are in relation to the cloud. If the cloud droplets change in size or shape, the effect is lost. According to the Cloud Appreciation Society, “iridescence can often occur in Altocumulus and Cirrocumulus clouds, but appears most often in lenticular clouds. The effect tends to be observed at the clouds’ fringes, but it can occasionally appear over large area.”
According to NASA, iridescence can be best seen outside the glare of the sun. The viewing is especially good when the sun is hidden behind thicker clouds, making the viewing safer. Frequently spotted directly around the sun. Below is a great example from NASA’s “Astronomy Picture of the Day”: