Izod clouds

Contributed by
Nov 26, 2007
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Regular readers know I am fascinated by sky phenomena; not just astronomy-related but also optical effects in clouds. A few days ago I was out with The Little Astronomer, and I noticed the clouds looked very odd; fuzzy, not well-defined, and very solidly white with almost no variation. My memory tweaked, and I slapped on a pair of polarizing sunglasses. Sure enough, bang! The edges of the clouds glowed pink and green, luminous, iridescent.

I call these Izod-Lacoste clouds, because I remember the pink shirts with the green alligator on them from when I was in high school. The clouds are a lot prettier:

Imagine my surprise when I found out that the day after I saw those clouds, Astronomy picture of the Day posted a picture of them... and the photographer (August Allen) shot it in Boulder! For all I know, that's the same cloud I saw.

The explanation for why the clouds do this can be found at the APOD page, or on this German weather site (it's in English). The wave nature of light is critical to making these colors, so it spurred a fun conversation with TLA about waves and interference (which is why polarizing glasses help; the light that comes off the cloud is highly polarized, so the glasses let that light through and block a lot of the glare from the cloud which otherwise drowns the colors out). Come to think of it, we never finished that talk... so now I have something to show her and talk about when she gets home from school today.

Tip o' the umbrella hat to BABloggee Kyle Carmichael.