The phenomenon is also called ‘mountain spectre’, since it most often occurs when the observer stands at a higher altitude on a mountain and sees their shadow cast on a cloud at a lower altitude.

A Brocken spectre within glory rings. Image credit: Brocken Inaglory

But a Brocken spectre can occur in any setting when the magnified (and apparently enormous) shadow of an observer is cast in mid air against any type of cloud opposite a strong light source.

Additionally, if the cloud consists of water droplets backscattered, a glory resembling a saint’s halo can be seen around the shadow of the observer’s head, caused by sunlight or (more rarely) moonlight interacting with the droplets. The glory consists of one or more concentric, successively dimmer rings that are always red on the outside and bluish towards the center. Due to its appearance, the phenomenon is sometimes mistaken for a circular rainbow, but the latter is much larger in diameter and is a result of different physical processes.

The below photograph is a good demonstration of the kind of setting in which a Brocken spectre occurs (the Sun is behind the observer’s head).

Image credit: Heini Samuelsen

The shadow’s apparent magnification is an optical illusion that occurs when the observer judges their shadow on relatively nearby clouds to be at the same distance as faraway land objects seen through gaps in the clouds, or when there is a lack of reference points to help judge its actual size.

The phenomenon draws its name from a local legend about the Brocken, a peak in the Harz mountains in Germany, where a combination of frequent fogs and low-altitude accessibility allows it to appear frequently. Giant shadows that seemed to move by themselves due to movement of the cloud layer (which is also part of a Brocken spectre by definition), and that were surrounded by glories, may have contributed to the reputation of the Harz mountains as land of witches and evil spirits, as reflected by the literature about the region.

The phenomenon can also occur around the shadow of a plane, for example. The position of the glory’s center shows that the observer was in front of the wings. Image credit: Brocken Inaglory

In order for the phenomenon to involve a glory, the clouds or fog causing it must be located below the observer, in a straight line with the Sun’s/Moon’s position in the sky and the observer’s eye.

For this reason, the glory is commonly observed from a high viewpoint such as a mountain, tall building or a flying aircraft, as shown above. In the latter case, if the plane is flying low enough for its shadow to be visible on the clouds, the glory always surrounds it. This phenomenon is sometimes referred to as ‘The Glory of the Pilot’.

Image credit: utkrixx/Reddit

But the ‘Glory of Nature’ seems to be a more apt title.