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The Brocken spectre is a bewitching optical phenomena that occurs when a low-lying sun casts a very long shadow into mist or fog in the distance. The effect creates a super-sized shadow figure, which looks three dimensional because of the depth at which the shadow descends into the mist. The specter is also frequently accompanied by a difficult-to-explain optical effect known as a glory, a rainbow halo that appears when light is refracted from uniformly sized airborne water droplets.
The Brocken spectre gets its name from a mountain peak called The Brocken, part of the Harz Mountains in Germany. The gently-sloping hills and frequent fog in this area makes the phenomenon easy to observe when conditions are right. The phenomenon was first described by Johann Silberschlag in 1780, but has probably been observed by confused humans ever since prehistoric times. It is unexplainable phenomena such as this that may have originally caused people to start thinking that the mechanics of the world were orchestrated by divine forces.
C. T. R. Wilson, a Scottish physicist responsible for the invention of the cloud chamber, which is used to observe particles of ionizing radiation, built the device when he was trying to artificially create the glory effect that accompanies Brocken spectre. The glory remains relatively difficult to produce in lab conditions to this day.
Under the right conditions, planes create Brocken spectres on underlying clouds. These are called the Pilot's Glory and helped inspire aerial fighters during WWII. In ancient China, the phenomenon was called "Buddha's light" and observations have been recorded as early A.D. 63. When pilgrims or monks saw their heads surrounded by glories from the Brocken spectre in the distance, they thought it signified that they were enlightened. A few fascinating videos of the Brocken spectre and glories are available online if you look around.