What is a Brocken Specter? Optical Phenomenon Explained as Images Go Viral

Mysterious photos of a rare optical illusion are going viral on social media, baffling people who have never heard of a Brocken specter.

Diane Doniol-Valcroze shared a photo of the phenomenon on Twitter and said: "A rare optic sight, the 'Brocken specter,' which occurs when a person stands at a higher altitude in the mountains and sees his shadow cast on a cloud at a lower altitude."

The photo was also shared on Reddit, where it received 127,000 upvotes.

The strange phenomenon amazed social media users, who are learning about the illusion for the first time. But what is a Brocken specter?

A Brocken specter, which is also called "anticorona, glory, Brocken bow, or mountain specter," is an illusion that can occur when someone stands on a hill that is partially covered in mist, in a position that their shadow will be cast onto the mist, according to the U.K. weather service, the Met Office.

This can create the illusion that their shadow is a person seen through the mist, and it will appear to be gigantic and at a distance.

The illusion occurs because the sun behind the person will project the shadow through the mist. The shadow will appear magnified due to an optical illusion that makes the shadow on the nearby clouds seem to be the same distance as landmarks that can be seen further away through the cloud.

The Met Office says that the shadow falls upon water droplets of varying distance, which distorts perception, making the shadow appear to move as the clouds shift.

"This all combines to make the rather disorienting effect of a giant shadow moving in the distance," says the weather service.

The term Brocken specter originates in Germany and is named after the Brocken, which is the highest peak in the Harz Mountains. The mountain is covered in clouds or mist for 300 days a year and is the subject of old superstitions.

Several Supernatural Sightings

The Brocken specter illusion is responsible for several "supernatural" sightings on Ben Macdui, the second tallest mountain in the U.K., located in the Cairngorms National Park, Scotland.

The Big Grey Man is a mythical creature described as a Scottish Big Foot, the legend of which came to prominence in the 1920s, as reported by the BBC.

At an annual gathering of the Cairngorm Club in Aberdeen, its honorary president, the highly respected mountaineer Prof. John Norman Collie, told a frightening story of an experience he had on the mountain 35 years previously.

Collie said he was climbing alone in the snow and mist and heard crunching sounds, and thought he was being followed by something large and ominous. But he ran away before he could discover what, if anything, was there.

Another climber, named A. M. Kellas, who was also a lecturer and veteran of Himalayan ascents, later told Collie that he had a similar experience on Ben Macdui. Then, other mountaineers said that they had not only heard, but had seen the Big Grey Man.

The visual phenomena have since been explained as being Brocken specters.