The phenomenon is also known as a “mountain spectre” because it most commonly occurs when an observer stands at a higher altitude on a mountain and sees their shadow cast on a cloud at a lower altitude.
A Brocken spectre, on the other hand, can occur in any setting when an observer’s magnified (and seemingly enormous) shadow is cast in mid air against any type of cloud opposite a strong light source.
Furthermore, if the cloud is made up of backscattered water droplets, a glory resembling a saint’s halo can be seen around the observer’s head, caused by sunlight or (rarely) moonlight interacting with the droplets. The glory is made up of one or more concentric, dimmer rings that are always red on the outside and bluish in the center. The phenomenon is sometimes mistaken for a circular rainbow due to its appearance, but the latter is much larger in diameter and the result of different physical processes.
The photograph below depicts the type of environment in which a Brocken spectre occurs (the Sun is behind the observer’s head).
The apparent magnification of a shadow is an optical illusion that occurs when an observer judges their shadow on relatively nearby clouds to be at the same distance as distant land objects seen through gaps in the clouds, or when there are no reference points to help judge its actual size.
The phenomenon gets its name from a local legend about the Brocken, a peak in Germany’s Harz mountains where frequent fogs and low-altitude accessibility allow it to appear frequently. Giant shadows that seemed to move on their own due to movement of the cloud layer (which is also part of a Brocken spectre by definition) and were surrounded by glories may have contributed to the Harz mountains’ reputation as a land of witches and evil spirits, as reflected in the region’s literature.
To include a glory, the clouds or fog causing the phenomenon must be located below the observer, in a straight line with the Sun’s/position Moon’s in the sky and the observer’s eye.
As a result, the glory is frequently seen from a high vantage point, such as a mountain, tall building, or flying aircraft, as shown above. In the latter case, the glory always surrounds the plane if it is flying low enough for its shadow to be visible on the clouds. This phenomenon is known as ‘The Glory of the Pilot’.
However, ‘Glory of Nature’ appears to be a more appropriate title.
John Ross Merritt says
So very very cool. Thank you so very much for the pictures and the great explanation. Being 68 years of age now I have always been curious. Sir David is a hero to me, and for you to give him credit for this picture allowed me to write a nice piece as part of my life story inspiring me in a fashion I had not known previously.