Monday, 6 February 2017
A colored patch under Moilanen arc
By Marko Riikonen and Jarmo Moilanen
These photos show a colored patch at the bottom of Moilanen arc. We don't quite know what it is. Nicolas Lefaudeux has suggested it could be a segment of circular "Moilanen halo". Such a halo has been photographed by Alexander Haußmann on 27. November, 2015, in Mt. Klínovec of the Czech Republic. Our display occurred in Rovaniemi on 16. December, 2015.
Or then it is the arc which has been observed under Moilanen arc a couple of times in relatively high light source elevation lunar displays. See for example the observation by Jari Luomanen. If so, then the explanation of this arc from rotating Moilanen arc crystals can't be right because the shape is wrong (the lamp is about 7 degrees below horizon).
There is also 9 and 35° halos - a pretty headache inducing combination were you to try a simulation. A crystal photo is provided. Looks like a lot of pyramids in it, but most are not really textbook pyramids. More crystal photos in the original report in Taivaanvahti.