A characteristically oval corona produced from diffraction by pollen grains. Two rings shine and the inner one has bright spots at 12 and 3 o' clock.
Beautiful images by Rafael Schmall at Somogy, ZseliciCsillagpark, Hungary
All images ©Rafael Schmall, shown with permission
Individual pollen grains diffract light. Incoming waves scatter from each point on the grain's surface. The outgoing waves overlap and interfere to form a diffraction pattern.
The diffraction pattern - corona - is non-circular with bright spots because the pollen grains are non spherical and are aligned in the air.
Many grains (not necessarily Rafael Schmall's) have air sacs to aid wind dispersal. These orient the grains very well. Others are oval and also orient to some extent.
The above image shows pine pollen with air sacs. Taken by Jari Luomanen.