Spectre of the Brocken, 1902.
© Science Museum / Science & Society Picture Library
Plate taken from G Hellmann's 'Meteorologishch Optik 1000- 1836' (1902). The meteorological phenomenon known as the 'Spectre of the Brocken' (Brockengespenst in German), is caused by diffraction of sunlight by water vapour droplets. It is named after the Brockenberg in the Harz Mountains of Germany, where legend has it, a walker fell to his death upon being startled by the phenomenon, known scientifically as an anticorona. Under the correct atmospheric conditions, the Sun casts a shadow of a person walking on a ridge onto clouds behind him. The shadow is magnified, and appears to move at the same speed as the walker, creating the illusion of a giant spectre stalking the person. The 'spectre' may also be surrounded by rainbow-like rings, as seen in the picture.