I have covered atmospheric optical illusions before in a previous post, and this week I came across another one: the Brocken spectre. According to Wikipedia, the Brocken spectre is “the apparently enormous and magnified shadow of an observer, cast upon the upper surfaces of clouds opposite the sun.” In addition to the shadow, the “head of the figure is often surrounded by the glowing halo-like rings of a glory—rings of coloured light that appear directly opposite the sun when sunlight is reflected by a cloud of uniformly-sized water droplets.”
Brocken specters will only appear under certain conditions. WeatherOnline summarizes them:
A Brocken Spectre can only be seen when specific conditions are met: The sun must be directly at one’s back and there must be many suspended water droplets in the air where the Spectre’s glory appears. Sunlight enters the water droplets and reflects off the back of the droplets and the light comes back towards the sun and the observer. This phenomenon is called diffraction and causes the circular rainbow-like bands around the shadow. Even if you are in a group you can only see your own shadow and glory (rainbow) ring, or your own Brocken Spectre. Therefore Brocken Spectres are confined to high-mountain areas when the sun is low.
Besides being an interesting atmospheric optical illusion, the Brocken spectre also has a dark legend behind it. WeatherOnline briefly describes the Brocken spectre’s sad origins:
Legend has that the name came from the Brocken, the highest peak of the Northern German Harz Mountains. Once a climber was startled by the sudden appearance in the nearby mist of a human figure with a ring of light around its head. Frightened, the climber fell to his death, killed by his own shadow that he saw and the ring of light was his own glory ring.
“Brocken Spectre” — WeatherOnline