Experimenting with Minnaert's Cigar.

We have studied the seldom-seen halo phenomenon that can arise in divergent light, Minnaert's Cigar, which we produced in laboratory experiments and computer simulation. In the laboratory experiments halos or transections were produced in clouds of alum crystals precipitated in a solution of ethyl alcohol or in alum crystals deposited upon glass plates. The three-dimensional cigar form was less pronounced in our small-scale experiments than when the form was observed over several meters. In our experiments and simulations transections through Minnaert's Cigar include different halo forms that may arise on window panes or windshields covered with halo-active ice crystals or as horizontal halos on glittering frost-covered ground.