Brocken spectre

The Brocken spectre is an optical illusion in which the apparently greatly magnified shadow of an observer, when projected onto a surrounding mist by a back light such as the setting Sun, interferes with that observer’s depth perception. The shadow is perceived to be further away than it is in reality when seen against a background of features known to be far away, and hence much larger than it actually is.^[1]

The phenomenon takes its name from the highest peak in the Harz Mountains of north central Germany, the Brocken, where it was first reported.^[2] The term was coined in 1780 by Johann Silberschlag, a German pastor and natural scientist.^[3]

Other manifestations of the illusion include the Grey Man of Ben Macdui – Am Fear Liath Mòr in Scottish Gaelic – a creature once believed to haunt the summit and passes of Ben Macdui, the second highest peak in the British Isles after Ben Nevis.^[4][a]Ben Macdui is in the Scottish Cairngorms.