Moonlight Lowitz Arcs
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Highlights
A rare sighting of a rare phenomenon. Three Lowitz arc components around a 22° parhelion plus a possible 46° arc.
Seen by Jari Luomanen (Facebook, Website) in a diamond dust display over Finland 10th February '17
Images ©Jari Luomanen, shown with permission
The bright coloured arc near the zenith might be a 46° Lowitz arc from rays passing between basal and side faces of Lowitz oriented plate crystals.
Lowitz arcs are drawn in red on this HaloSim ray tracing. To show the middle arc, relatively thick plates were used with restricted rotational positions about the Lowitz axis.
Tobias Lowitz drew arcs extending downwards from sundogs in a halo display over St Petersberg, Russia in 1790. Then followed a long interregnum for Lowitz's arc was not confirmed until the 1990s.
One possible reason is that searchers were looking in the least favourable place.
The most commonly seen Lowitz arc is the upper one extending above the top of the 22 degree halo to touch a Parry arc. Arc sightings near sundogs are much more rare and even then they are usually faint and poorly defined.
That makes Jari Luomanen's moonlight sighting the more spectacular. There are clear upper and lower arcs and there is a rarer faint middle arc passing upwards through the parhelion itself.
