Brocken spectre
Concise Oxford English Dictionary © 2008 Oxford University Press:
Brocken spectre/ˈbrɒk(ə)n/
▶noun a magnified shadow of an observer thrown on to a bank of cloud in high mountain areas when the sun is low.
– origin C19: named after the Brocken, the highest of the Harz Mountains in Germany.
'Brocken spectre' also found in these Oxford entries:

