Moon Corona pictured in Sweden 22nd December 2010 by P-M Hedén (Clear Skies - Astro & Sky Images, TWAN member). ©P-M Hedén, shown with permission.
Atmospheric
Optics

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P-M's composite image - 0.8s for the corona and 1/1300s for the moon tells us much.  It reveals the subtlety of coronal colours each hue a complex mixture rather than the purer colours of a circumzenithal arc or rainbow.

It gives the angular diameter of the rings. Comparison with a Mie scattering calculation by IRIS shows that the cloud droplets diffracting light were about 20 micron (0.02mm) across.

And the exposure ratio of 1000:1 speaks of the enormous brightness difference between a corona and its light source, almost impossible to span in a photograph but one that human eyes handle easily.