by Antonino Gumina, Milan, Italy.
shown with permission.
All very small cloud droplets and ice crystals scatter
light waves to produce colours at particular angles from the sun.
Why then are clouds white or at least not full of iridescent
In thick clouds most sunlight is scattered by many droplets. The angular
information is lost and the colours mix to white.
Most mature clouds have a range of droplets sizes and, again, the colours
are smeared out to white.
But when clouds are freshly formed and thin their droplets have similar
sizes and many sun rays only interact with one drop. Then we see the
iridescent colours that tiny drops and crystals always produce.