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This phenomenon, named after the German mountain range where it was first observed, consists of the vision of clouds or fog casting a large shadow.
When conditions are right, a person's shadow can appear gigantic and surrounded by a colourful halo.
This effect is due to the scattering of light on water droplets or fog particles in the air.
The light refracts and reflects off these particles, creating a fascinating optical illusion.
The explanation is that the sun shining behind the observer casts a shadow through the fog, and the magnification of the shadow is an optical illusion that makes the shadows of nearby clouds appear to be at the same distance as the distant landmarks seen through the clouds.
In addition, the shadows reflected by water droplets at different distances distort perception and make them appear to move as the clouds change.
All this combines to create the rather disorienting effect of a giant shadow moving in the distance.