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[German: ‘holy light’]

A bright, colourless fringe of light surrounding the shadow of an observer's head, i.e. around the antisolar point. There are two separate mechanisms, the strongest being when sunlight falls on dew-covered grass. The dewdrops and blades of grass act together as retro-reflectors, returning the light preferentially towards the source. The second, weaker effect (known as a hot spot in aerial photography) occurs with a rough surface, such as dry grass or leaves. An observer looking at the antisolar point does not see the shadows of the leaves, which are masked by the objects themselves. Every visible surface is fully illuminated, so the immediate vicinity appears brighter than the surrounding area, where the shadows come into view.

Subjects: Meteorology and Climatology.

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