Lunar Fogbow, Finland

A rare and beautiful sight Imaged by Thomas Kast (Salamapaja). The broad and colourless fogbow has an inner supernumerary fringe. The bows themselves do not reflect in the water, different fog droplets produce the reflected bows.
Fog droplets are small (1-100 micron diameter). They are sufficiently close to visible light wavelengths (0.4-0.7 micron) that diffraction effects are significant.

The result is a diffuse and wan bow rather than the sharp bright hued rainbow from much larger raindrops.
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Each droplet reflects and diffracts incoming plane waves backwards to form the fogbow rings.

Waves scatter in other directions to simultaneously form the glory and corona.