Tuesday, 6 January 2009
Divergent light curiosities
In the image above the two photos in rigth hand column represent intense pillarforests with superparhelia rising from nearby lamps. The sight is very impressive as tens of lamps around the observer create pillars. Furthermore, one can see a long circumzenith arc, as all the lamps contribute to it ( 1 ).
Some interesting halo geometries come about when one approaches a spotlight and the light rays become ever more divergent. In the leftmost column there are two examples of that. In the upper photo both car headlights are the light source, and peculiar arcs are formed each side of the lamps. A strong feeling is that these are superparhelia-related. In the lower photo the camera is only 5 meters from the spotlight and almost outside the strongest beam. The shape of the subparhelia gets distorted in a funny way. That effect can also be seen in Jari Luomanen's photo ( 2 ).
So far we have no definite answer to the origin of these halos, but surely they are a result of quite complex geometries involved in divergent light scattering and represent distorted images of ordinary haloforms. These photos are important in correctness evaluation of divergent light simulation code. Should anyone reading this want to shoot similar images, I suggest that the relative distances are carefully noted so that comparison with simulations can be done.
During the night between 2nd and 3rd January the divergent-light 120° parhelion was seen as well ( 3 ) and some crystals were collected and photographed at the same time ( 4 - 5 ).