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.