I was driving home from getting some lunch and about 4 blocks from my house I noticed these iridescent clouds around the sun. When I first saw them they were the most vibrant ones I had ever seen. By the time I got my camera out and found a clear view they had diminished in vibrancy quite a bit, but were still fairly impressive.
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From Wikipedia: Iridescent clouds are a diffraction phenomenon cause by small water droplets or small ice crystals individually scattering light. If parts of clouds have small droplets or crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, and newly forming clouds produce the brightest and most colorful iridescence.