On 29 December 1996, I observed in a
very clear sky a corona around the Sun
consisting of 3 concentric rings. This
phenomenon increased the optical depth
of the atmosphere by about 0.03 at 1020 nm.
I am located in South Central Texas.
Knowing the diameter of the innermost ring, it
is possible to estimate the size of the particles
causing the corona at about 60 microns. I therefore
assume that the corona was caused by pollen from
the dense stands of "mountain cedars" (actually junipers) in
the Texas Hill Country. I would very much appreciate
receiving information about the diameter of pollen
grains from this tree. Thank you.
Forrest M. Mims III
Sun Photometer Atmospheric Network (SPAN)