Cloud iridescence

Nature is filled with astonishing beauty, phenomena that simply takes our breath away when we are fortunate enough to bear witness to them and one such occurrence which we have been fortunate enough to have been privy to on two occasions was something called cloud iridescence.

This is a magnificent display of the properties of diffraction of light caused by especially tiny water droplets or ice crystals individually scattering the white light entering a cloud. The droplets/crystals must be the perfect size within the cloud and at the perfect angle to the sun to be able to promote this phenomenon and so it is quite a special thing to see when it does happen.

This occurrence is completely different to a rainbow in that as you see above the colour is actually within the cloud and not in front of it as with a traditional rainbow. Interestingly enough, the name iridescence or irisation comes from the Greek word “Iris” which was the Greek personification of the rainbow.

Their formation is usually observed in very thin, spread out clouds such as altocumulus, cirrocumulus and especially lenticular clouds. The more uniform the droplets or crystals within the cloud formation, the greater the diffraction and larger the visible iridescence.

If the crystals within the cloud were a slight bit bigger, they would not produce iridescence but rather a halo which is a completely different phenomenon but almost equally as beautiful.