WHAT IS A BROCKEN SPECTRE AND GLORY?
A Brocken Spectre occurs when the observer casts his or her shadow on a wall of fog. The wall of fog can be compared with a screen in a cinema, where the shadow is projected on, and magnified several times. But contrary to the screen, fog has no smooth (real) surface, so that it causes three-dimensional pictures which move in a spooky way by the waving of the fog, although the observer does not move at all. Sometimes there forms a colourful, annular optical phenomenon around the “head” of the spectre of the Brocken, which is called a glory. This glory is caused by backward scattering and diffraction of the sunrays by the very small fog droplets. The rays of light become diverged by the small round droplets into a pattern of concentric circles. The larger the distance between observer and the fog is, the bigger and more colourful the glory becomes, but the spectre of the Brocken becomes smaller and fainter. But on the other hand, another phenomenon often becomes visible:the fog bow.
