The apparently greatly magnified shadow of an observer cast on to the surrounding mist. The effect is an illusion. Depth perception is altered by the mist, causing the shadow to appear more distant and to be interpreted as larger than normally expected. Named after the Brocken, a peak in the Harz Mountains in Germany, with which the effect is associated.
From: Brocken spectre in A Dictionary of Weather »
Subjects: Science and technology — Earth Sciences and Geography