Suppose we are on a hill, and behind us the Sun or the full Moon is shining. Our shadow is projected onto the fog below and is apparently transformed into a pyramid-shaped silhouette with its apex at the antisolar point, right where the shadow of our head appears. This shadow is called the Brocken Spectre and the term was coined during observations made in the Harz Mountains in Germany. If the apex of the shadow is outlined by a bright halo, then the Glory is observed. Observations of the phenomenon are mostly made from aircraft in flight. The glory is an anthelion, i.e., a phenomenon that occurs in the direction opposite the star. Often the Spectre can be highlighted and accompanied by a white rainbow in the fog (fogbow) as well as by a Glory. Our shadow seems very extended but at most it cannot exceed thirty meters in length. In the past, attempts to interpret this phenomenon were “mystical”; in fact, holiness was attributed to the person whose head was surrounded by the halo. The spectre is also visible at night with artificial light sources such as a car’s headlights or a very powerful torch.
According to physicist Robert Greenler, the halos drawn around the heads of Saints in art history seem to be an interpretation/reproduction of the physical phenomenon of the Glory.
The theory formulated by Van De Hulst H. C. (in “Light Scattering by Small particles”, New York, 1957) states that the rings of the Glory are formed by tiny droplets and ice crystals belonging to cirrus clouds or fog; according to this study, the radius of the concentric rings can vary from a minimum of 1.2° to a maximum of 8.3°.
Photography:
To photograph this rarity it is best to use the same precautions useful for halo phenomena. In addition, to increase the contrast of the glory, it is advisable to use short telephoto lenses, such as a 100mm. If instead you want to capture the fogbow too, a fisheye, an 18 mm f/2.8 or a 20mm f/2.8 would certainly be fine. Generally, to photograph all photometeors it is recommended to always take a series of three shots for each lens to be used; the three shots should be taken underexposing by ½ stop, exposing correctly, and overexposing by ½ stop, so as to always ensure a good margin of success.
Pilot’s Glory (by Massio Poggi )
Glory and Brocken Spectre
In conclusion:
Many think that the Glory and the Spectre are the same phenomenon, but that is not the case. They are two different and distinct phenomena: the Spectre is simply the observer’s shadow, while the Glory is made up of the halo and the concentric rings visible within it. The details of the Glory in this photo are not visible. The Spectre could be comparable to an anticrepuscular ray formed by the photographer’s shadow.
Bibliografia nei testi consigliati
