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Fog rays and God rays – optical phenomena at fog margins

A phenomenon occurs at fog margins which goes by a variety of popular names, including God rays, sunbeams, fog rays and Buddha rays. The technical term is Crepuscular rays.


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In dense fog, where visibility can drop below 100 m, there are no shadows nor direct sunlight. In the diffuse lighting, contrasts disappear and the landscape takes on a mystical air.

Close to the top of the fog band, however, the situation changes abruptly. The light rapidly gets brighter, and the sun is initially seen as a disc, which then quickly becomes dazzlingly bright. This is the time to look towards the sun through the trees. The sunlight shines through the backlit tree, but is partially blocked by the branches and leaves.

In the areas that are illuminated by the sun, the light beams are scattered by the small fog droplets. This creates a spotlight-like effect, and the observer has the impression of seeing the sun's rays. In some instances, the shadow of an object or a building is projected onto the screen of the fog.