Cool Cloud Iridescence
We were leaving the grandkids’ softball game this evening just before sunset. As we were waiting to go to the car, a cool iridescent cloud caught my attention. When I first spotted it, the cloud was more rainbow like, but by the time I got out my phone to take a picture, it wasn’t as bright. Still, it was cool. I’ve seen them much more vivid, but this was after there not being a single cloud in the sky for an hour or so.
irisation is caused by uniform droplet size in the clouds, diffracting light from the sun. It occurs within ten degrees of the sun. The clouds have to be thin enough that the sun is only diffracted through a single water drop to get the rainbow colors. These clouds were just forming, so they were thin enough to cause the irisation. They were also just above the setting sun which was just below the trees, so the sun was at a good angle for the light to diffract