|Lunar Halos ~ Dec 3 Imaged by Marko Mikkilä at Sotkamo, Finland. Marko's website, halo images. ©Marko Mikkilä, shown with permission.|
|Last Thursday night showed the best lunar halo displays that Marko Mikkilä had ever seen. Marko had made a special 6-700 km round trip up north to be in the vicinity of ski-slope snow machines because downwind of them can be found diamond dust crystals of superb optical quality. It was worthwhile!
The large image is dominated by a 22 degree halo from randomly oriented crystals. At just over twice the distance from the moon is a much less common sight, a 46° halo.
Touching the inner 22° halo at top and bottom is a circumscribed halo from horizontal column crystals. Columns also produced the colourful infralateral arcs and the paraselenic circle. That there are no moon dogs (paraselenae) tells us there were few plate crystals.
The all-sky view (2) and the unsharp masked version (3) show more column arcs, Wegener arcs and, very unusually, a complete subhelic circle (subselenic in this instance?). The HaloSim ray tracing identifies the arcs but does not reproduce the complete subhelic circle - special crystals are probably needed for that.
More of Marko’s images taken that evening (see the set) show column arcs. Image 4 has a splendid lower tangent arc produced earlier in the evening. There are also traces of 'flared' pillars above artificial lights. Image 5 shows the flares clearly. They are spatial halos, the result of nearby horizontal columns.
Finally (5) a combination of lunar halos and those from a high intensity lamp!