Iridescent Clouds and the corona

  Iridescence and coronae are similar phenomena. Coronae result when the droplets are similar in size over a large area of sky near to the sun. Iridescence demands droplets locally similar in size but their mean size can vary across the cloud. If it varies smoothly the colours are banded, otherwise they are irregular. Lauri Kangas (site) watched this iridescence change from the corona like structure at right to the broadly banded colours at left. ©2004 Lauri Kangas, shown with permission.