About a week ago, just having started our descent, we experienced something pretty cool. And luckily I had my phone in hand to catch it on camera. It’s a rare penomina called a brocken spectre.
A brocken spectre appears when the sun shines from behind an observer, who is looking down into mist, fog or cloud. The phenomenon can appear on any misty mountainside or low cloud bank when hiking, or can be seen from an airplane descending into cloud with the sun shines directly behind them.
It appears as an enormous and magnified shadow of the observer or plane, cast upon the clouds. The shadow is surrounded by the glowing halo -like ring of coloured light.
The name brocken spectre comes from a peak called brocken in the Harz mountains in germany where this phenomonon is first observed and desciped by Johann Silberschlag.
Up until 2003 no really clear explanation had yet been given, but a deeper mathematical analysis revealed that the main cause is a tunneling effect of incoming light on the surface of the water droplets, an effect which is not necessary in order to explain rainbows for instance. In other words, a part of the light from the sun which passes very close to a droplet actually goes in the droplet thanks to a tunnelling effect, and is sent back in the direction it came from via usual optical phenomena, including wavelength separation of colors, hence the appearance of multiple concentric rainbows.