They are often bright white; they can be grey or even quite dark. But how about pastel-shaded clouds?
I didn’t see them, but many did. I received more than half a dozen photos of an optical phenomenon known as “cloud iridescence.”
Cloud iridescence is a fairly rare phenomenon usually seen in altocumulus or high cirrus-type clouds. The colours in the cloud are similar to those seen in soap bubbles or oil on the road after a rain. The lovely display can also be described as cloud irisation; that term comes from Iris, the Greek personification of the rainbow.
Here’s what happens:
When parts of clouds are thin and have similar-sized droplets, diffraction can make them shine with stunning colours. These colours are usually found in random patches or bands. Iridescence is usually seen in the edge of a cloud that is forming; that’s where the droplets will have a similar history and therefore a similar size.
Because these pretty pastel patches are usually found in the vicinity of the sun, they’re often hard to see. It’s never a good idea to stare directly into the sun, so the best way to see an iridescent cloud is to place the sun behind a foreground object, like a building or a large tree.
Look up, but always remember to protect your eyes!
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Cindy Day is the chief meteorologist for SaltWire Network.