Goethe’s Faust is a tale of the supernatural. According to a famous passage, on Walpurgisnacht a witch’s sabbat was celebrated on top of the Brocken, a mountain in the Black Forest. Old maps show this point circled by witches on broomsticks. Although probably not a very ancient tradition, it grabbed the imagination of 19th century romantics. They claimed at certain times magical visions could be seen from the peak. Even though no witches were visible on the mountain, gigantic shadowy figures were projected onto the clouds; the Spectre of the Brocken.
According to the Encyclopaedia Britannica “this phenomenon is often observed on mountain peaks” but even the non-supernatural explanations seem unbelievable. According to the Britannica “When the sun is low, shadows cast by the sun become magnified and seemingly gigantic silhouettes are cast on the upper surfaces of low-lying clouds or fog below the mountain.”
A later entry is contradictory: “The apparent magnification of size is an optical illusion that occurs when the observer judges his shadow on nearby clouds to be the same distance as faraway objects seen through gaps in the clouds.”
So is the magnification real or an illusion? As the sun’s rays are practically parallel, any shadow cast by the sun remains the same size as the object. Thus a shadow at even a modest distance from the observer can only seem small. In justification Britannica mentions the common sight of an aeroplane’s shadow cast on clouds beneath, but a jumbo jet casts a decent sized shadow, a human sized shadow would be insignificant.
In spite of many literary references (De Quincey for example) first-hand accounts of “the Spectre” by first-rate observers seem non-existent. (Does any reader know of any?). But some accounts state that the figures seem frightened of the observer and rush away as soon as they are seen.
The whole thing seems ridiculous, or so I thought until I saw the phenomenon myself in New Zealand. In fact I have observed this effect twice-which considering the time I have spent in the mountains, implies it is a relatively rare event.
The first occasion was when climbing a ridge above the Wangapeka River in what is now Kahurangi National Park. The sun rose over another ridge behind us and gigantic shadow figures appeared on the hillside across the valley. Before I had fully grasped what was happening they had shrunk down to normal size, where they were just visible. At least that explained the accounts of figures “rushing away”, they simply got smaller, and very rapidly too.
The explanation was quite obvious to anybody with some knowledge of optics; light is refracted when passing over an edge. The first gleam of sunlight over the ridge was bent into a widening beam that produced a huge shadow as effectively as a point of light projects an enlarged shadow onto a screen. The bush-clad hillside opposite us acted as a screen on which we could see the projection. But as the sun rose, the refraction diminished until enough of the sun was visible to produce the normal parallel rays with which we are familiar. So the initial large shadow quickly shrank to normal size.
Was this illusion awe-inspiring? Was it even an illusion? Were we frightened? Was it immediately obvious that we were observing our own shadows not supernatural entities? Well no, no, no, and yes. My wife, the complete skeptic, summed up, “Why make a fuss about shrinking shadows?”
I am confident that I can explain the reports of run-away shadows in mountain regions. The conditions necessary for observing this phenomenon seem to be that the sun must rise over a not too distant sharp edge, the air should be still and very clear. The observers be on a minor peak or ridge, and the projection be onto a fairly plain surface.
Does this explain the “Spectre of the Brocken” better than the Encyclopaedia? Well to be honest, no. The Brocken is the highest mountain around. So how could the sun rise over a sharp edge unless other peaks are very close? I doubt that clouds can ever have sufficiently sharp edges to produce the effect.
Perhaps the Spectre of the Brocken is as real as the reports there of witches, while its magical reputation has seen it acquire stories of phenomenon that are real in other mountainous areas.
