Dec 11 2013


Published by at 7:12 am under Weather & Sky

Iridescent cloud (photo by "not on your nelly," Creative Commons license on Flickr)

There are a lot of iridescent things in nature:  birds, beetles, seashells, fish, minerals and clouds.

Yesterday, after a snowy start (and really bad traffic!) the wind swung around to the west and the sky cleared with a few fast-moving clouds.  At lunchtime I looked up while standing in a building’s shadow and saw a thin, beautiful, iridescent cloud blowing past the sun.

Thin is important.  Iridescence occurs when sunlight diffracts through a thin layer of water droplets (or ice crystals) of uniform size and orientation.  The glowing colors are named for the Greek goddess Iris, the personification of rainbows.

Pittsburgh’s iridescent clouds aren’t nearly as cool as the nacreous clouds in Antarctica, but we don’t have the super-cold stratospheric temperatures that cause those clouds. For which I am grateful!


(photo by “not on your nelly” on Flickr, Creative Commons license. Click on the image to see the original)

One response so far

One Response to “Iridescent”

  1. Robon 11 Dec 2013 at 9:20 am

    Yes, but this morning was a good approximation of Antarctica, at least too close for me. I’m gettin’ too old for this stuff 🙂 BRRRRRRRR!

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