Aureoles on April 20th and 21st, 2009
On April 20th and 21st aureoles around the sun with reddish rims could be seen at Trier. They were larger and most prominent on April 20th and probably due to large amounts of pollen in the air. Larger plant particles could be seen hovering in the air, but these were too large to produce the aureole. The aureoles of April 20th point to a particle size of 20 micron, which corresponds nicely to pollen grains. Windows and cars were covered with a layer of green pollen dust. At sunset, faint oval coronae were still visible.
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