This Rare Optical Sight Called 'Brocken Spectre' Occurs When Your Shadow Is Cast Upon A Cloud Opposite A strong Light Source

The phenomenon is also known as a “mountain spectre” because it most commonly occurs when an observer stands at a higher altitude on a mountain and sees their shadow cast on a cloud at a lower altitude. A Brocken spectre, on the other hand, can occur in any setting when an observer’s magnified (and seemingly enormous) shadow is cast in mid air against any type of cloud opposite a strong light source.

The phenomenon gets its name from a local legend about the Brocken, a peak in Germany's Harz mountains where frequent fogs and low-altitude accessibility allow it to appear frequently. Giant shadows that seemed to move on their own due to movement of the cloud layer (which is also part of a Brocken spectre by definition) and were surrounded by glories may have contributed to the Harz mountains' reputation as a land of witches and evil spirits, as reflected in the region's literature.