A spooky spectre looms out of the fog in the Tatra mountains in Poland -- but it isn't a ghost. It's an example of a rare optic phenomenon which occurs when an observer standing at a higher altitude sees his own shadow cast onto cloud below him. As here, the shadow is often encircled with colored rings caused by diffraction of light by water droplets. The phenomenon is called a 'Brocken spectre' after a peak in the Harz mountains in Germany, where the first recorded sighting occured in 1780. According to an old mountain climbers' superstition, whoever sees a Brocken spectre will one day die in the mountains.