June 05, 2002
As small compensation for persons suffering from allergies, nature provides some interesting phenomena observed when sunlight is scattered by pollen. When pollen counts exceed 2000-4000 particles per cubic meter, difraction rings of colored light known as pollen corona can be observed around the sun. Pine and birch produce the best corona, as well as alder, hazel, walnut, barley, spruce and rape. Above is the first photo of birch pollen corona observed in Cologne, Germany. Pollen morphology varies among species, and irregularly shaped pollen (such as pine) will produce non-circular corona.