Optical coronae and iridescence: some simple hands-on activities

In this article we put forward a simple idea to demonstrate cloud iridescence. The activity is aimed at upper level primary school children and above, to see that some oft-observed optical phenomena in real life are the result of diffraction through droplets on a surface or in a cloud. We use the example of polar stratospheric clouds which displays the phenomenon of iridescence. A simple hands-on activity is explained whereby spherical droplets in a cloud are modelled by small glass beads suspended in silly-putty and the iridescence effect arises from a non-uniform size distribution of these beads.