A Brocken spectre also called Brocken bow, mountain spectre or glockenspectre is the apparently enormous and magnified shadow

Shadow

A shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the...

 of an observer, cast upon the upper surfaces of clouds opposite the sun. The phenomenon can appear on any misty mountainside or cloud bank, or even from an aeroplane, but the frequent fogs and low-altitude accessibility of the Brocken, a peak in the Harz Mountains in Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, have created a local legend from which the phenomenon draws its name. The Brocken spectre was observed and described by Johann Silberschlag

Johann Silberschlag

Johann Esaias Silberschlag was a German Lutheran theologian and natural scientist from Aschersleben, Principality of Halberstadt....

 in 1780, and has since been recorded often in literature about the region. However it can be seen in any mountain region.

Occurrence

The "spectre" appears when the sun shines from behind a climber

Mountaineering

Mountaineering or mountain climbing is the sport, hobby or profession of hiking, skiing, and climbing mountains. While mountaineering began as attempts to reach the highest point of unclimbed mountains it has branched into specialisations that address different aspects of the mountain and consists...

 who is looking down from a ridge or peak into mist

Mist

Mist is a phenomenon of small droplets suspended in air. It can occur as part of natural weather or volcanic activity, and is common in cold air above warmer water, in exhaled air in the cold, and in a steam room of a sauna. It can also be created artificially with aerosol canisters if the...

 or fog

Fog

Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...

. The light projects the climber's shadow forward through the mist, often in an odd triangular shape due to perspective

Perspective (visual)

Perspective, in context of vision and visual perception, is the way in which objects appear to the eye based on their spatial attributes; or their dimensions and the position of the eye relative to the objects...

. The apparent magnification of size of the shadow is an optical illusion

Optical illusion

An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...

 that occurs when the observer judges his shadow on relatively nearby clouds to be at the same distance as faraway land objects seen through gaps in the clouds, or when there are no reference points at all by which to judge its size. The shadow also falls on water droplets

Drop (liquid)

A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant drop...

 of varying distances from the eye, confusing depth perception

Depth perception

Depth perception is the visual ability to perceive the world in three dimensions and the distance of an object. Depth sensation is the ability to move accurately, or to respond consistently, based on the distances of objects in an environment....

. The ghost can appear to move (sometimes quite suddenly) because of the movement of the cloud layer and variations in density within the cloud.

The head of the figure is often surrounded by the glowing halo-like

Halo (religious iconography)

A halo is a ring of light that surrounds a person in art. They have been used in the iconography of many religions to indicate holy or sacred figures, and have at various periods also been used in images of rulers or heroes...

 rings of a glory

Glory (optical phenomenon)

A glory is an optical phenomenon that resembles an iconic saint's halo about the shadow of the observer's head. The effect is produced by light backscattered towards its source by a cloud of uniformly sized water droplets...

, rings of coloured light that appear directly opposite the sun when sunlight is reflected by a cloud of uniformly-sized water droplets. The effect is caused by the diffraction

Diffraction

Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

 of visible light.

External links

• "What are Brocken Spectres and How Do They Form?", an article on the Online Fellwalking Club page