On April 9th, 2014, Uwe Bachmann observed a pillar of light, produced by sunlight falling onto the building of the European Central Bank (EZB) in Frankfurt. He was observing from the German Weather Service’s (DWD) headquarters in Offenbach, i.e. from a distance of 3 kilometers.
For his first photo taken at 6.17 UTC, the sun was at an elevation of 13.9° and at an azimuth of 94.8°. The upward beam of light is thought to be produced by reflection from the building’s front, which is at an angle of 9° to the vertical, with scattering from aerosol producing the luminous pillar.
With the rising of the sun and the changing of its azimuth, this pillar is “cut down” subsequently. The second photo shows the situation at 06.35 UTC for a solar elevation 16.8° and an azimuth of 98.4°. The skewness of the reflected beam of light at an angle of 45° is evident.
The last photo taken at 06.52 UTC for a solar elevation 19.5° and an azimuth of 101.8° shows the beam being reflected almost at a right angle. Here, the azimuth of the sun is almost coincident with the observer’s.
Author: Michael Großmann,Kämpfelbach & Uwe Bachmann DWD, Offenbach, Germany
In August 2013, Ujj Ákos from Bátonyterenye in Hungary noticed light phenomena in a mosquito net for several times. There were phenomena visible (1–2–3–4) which resembled halos, similar to those in a spider web which Christoph Gerber photographed, but also iridescent colours were visible (1–2). Unfortunately, it is difficult to see what exactly causes the brightenings, although one can assume that they are caused by forward scattering of light along the different threads. But a mosquito net has no radial structure. So the reason of the phenomena probably lies in the grating of the net causing colourful light diffractions.
Diffraction patterns in fabrics can differ significantly and depend from the material used and its mesh. So crosses and paths of light are formed like those in this picture, or different kinds of coronae which can be seen here.