Brocken specter, or Spectre of the Brocken, is the name given to a pretty nifty optical illusion that was first observed on the Brocken peak in Germany, earning it the local name Brockengespenst. It happens when a person or object creates a shadow that then gets a leg up by casting onto a cloud or mist. The combination results in an enormous shadow that looks really far away, and occasionally moves even if the person or object casting it remains still.
If you weren’t aware of the mechanism behind it, seeing such a thing might make you believe in specters, aka ghosts. Photos of Brocken specters show how they extend and widen the legs and arms of their creators, giving those behind them the alien-like appearance of radioactive Mr Burns emerging from the woods.
Their outline gets warped as the sun projects their shadow into the three-dimensional cloud or aggregation of mist. From the position of the person casting it, the magnification of their shadow onto the nearby cloud makes it look as if it’s being cast to far-reaching parts of the landscape, making them look enormous.
Better yet, clouds are dynamic entities and as their water droplets shift so too can the shadow making it move. The effect gives the entire ensemble a rather psychedelic feel as your silhouette creates a groovy, waving shadow giant. It’s effectively nature’s very own Wacky, Waving, Inflatable-Arm-Flailing Tube Man.
The technicolor cherry on top of the optical illusion is the appearance of a halo, or glory, which appears like colorful rings around the shadow of the head. It happens when light interacts with water droplets, creating concentric rings that shift from red to blue resembling something like a rainbow dartboard. While glories are formed through a similar process to rainbows, they are different in that the angle of a glory from its source is much smaller meaning the light diffracts, reflects, and refracts in water droplets at different angles.
If you want to have a go at making your very own Brocken specter, the best way to find suitable misty opportunities is hiking. A good place to start is the optical illusion’s namesake, the Brocken peak in the foggy Harz mountains of Germany. Occurrences here have been common since Johann Silberschlag first described Brocken specters back in 1780. However, if the Brocken isn't exactly in walking distance you can also head to any high up place which is partial to foggy, cloudy weather with a spot of sun.
Happy giant making!