Lunar Corona, Croatia

A capture by Marko Posavec from the summit of Ivanščica mountain in northern Croatia, 1061m (3480 ft) above sea level.
The gibbous moon was near the Pleiades which are to its left.

©Marko Posavec, shown with permission

Water droplets scatter light in all directions.

Backward scattering gives a glory opposite the sun or moon. Waves scattered ~40° from the backwards direction give a fogbow.

Waves scattered almost forwards along the direction of the incident light are responsible for the corona. These waves come mostly from the droplet periphery.

The corona diffraction pattern is larger the smaller the droplets and hence can give information on the size of droplets that created it.

The camera and lens details at left yield the diameter of the second red ring as about 10°. At right the corona is matched against an IRIS (Mie-Lorentz) simulation with a droplet diameter of ~18.4 micron.

Fog and cloud droplets are 1 to 100 micron dia. As fog ages the average droplet size tends to increase and the size distribution broadens.

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"We had been stuck under a high pressure area for days, which caused the temperature inversion and the fog layer covering the lowlands.

Up on the mountain, however, the sky was clear until nightfall when thin wisps of fog, probably comprised of very small water droplets, started crossing over the summit.

As they did so, a bright corona with multiple rings appeared around the gibbous Moon. The show was so great I could hardly believe my eyes. It was not long, however, before the fog obscured everything.

Photo details:
Olympus E-5, with Zuiko 11-22 mm lens at 11 mm focal length, 25 seconds exposure, f/5.6, ISO 200. Some lens artifacts are visible due to the brightness of the Moon. The picture doesn't do real justice to the visual show. It was simply spectacular."