Pileus clouds are rare, but they are a sight to behold when they form. Like this one, shot earlier this month in Pu’er, Yunnan Province, China.

These clouds get their name from their Latin name, which means “cap.” Call it rainbow magic, but these “scarf clouds” form on top of other cumulus clouds.

The science behind the iridescent colors

Pileus clouds are thinner than cumulous clouds and contain uniform-sized droplets. The smaller the droplets, the more iridescent the colors.

Pileus clouds are usually a sign that a thunderstorm is brewing.

If you’re lucky enough to see a pileus cloud, take a moment to appreciate the rare beauty of this phenomenon. See more Iridescent Pileus clouds below.