nubbsgalore:

iridescent pileus cloud photos by esther havens in ethiopia, becky bone dunning in jamaica, ken rotberg in florida, and david lapuma.  as a cumulus cloud containing warm air convects upwards and condenses, a thin layer of humid air containing water vapour is thrust above the cloud, cooling from the lower pressure into droplets, which, when small enough and uniform in size, diffract light from the sun when it’s at least fifty eight degrees above the horizon.