Strange, mysterious things can happen in the mountains. Among the more scientifically explainable phenomenon one may encounter at high altitudes is the Brocken spectre. These unnaturally large shadows show up on clouds, shifting fast and decorated with rainbow halos.
These shadowy figures are named for the Brocken, a mountain peak in the Harz Mountains of Germany. Due to its height, the peak often extends above low cloud or fog cover. The spectre appears on these clouds below the viewer when the sun is shining behind their back. It usually appears as a larger-than-life shadow of somewhat triangular shape. Rainbow rings radiate from the shadow.
So how do these rare optical illusions come to be? Scientifically, this effect is fairly easy to explain. The sun causes a shadow to fall upon (and through) the water droplets of the cloud or fog. The distance of the shadow makes it hard for the viewer to accurately judge the size and proportions of the shadow. The colorful solar glory often seen around the shadow is produced by light refracting within the water droplets. As clouds shift, the Brocken spectre can seem to flicker and move.
Brocken spectres are often seen at high altitudes in nature, and they have received much attention since first being described in the late 18th century. They have been mentioned by the likes of Charles Dickens, C.S. Lewis, and the psychiatrist Carl Jung. The figure often appears in literature as a haunting reflection of one's troubled self. In real life, some speculate the phenomenon may have contributed to supposed sightings of Bigfoot and yeti creatures. The Brocken spectre continues to fascinate today as an elusive optical phenomenon.