Wednesday, 3 December 2008
Lascar display III
Continuing the Lascar halos tour. This image gives situation for sun elevation range of 11° to 9°. Image is stacked from four photos and also mirrored version is provided. 23° plate arc is already disappearing high up above the sun, but 20° upper plate arc on the other hand is appearing.
10 years ago we simulated the display with octahedral crystals of cubic ice and traditional pydamidal crystals. Octahedral crystal gives halos only at 28° and 19° from the sun. It was a good candidate for simulating because many features in photos from different solar elevations fell in place with it.
Among other things these simulations predicted that the 20° upper plate arc would be actually composed of two arcs, the other one being 19° upper arc... But there are still too many unexplained features in the display to trust our model, one being the fake 18° plate arcs.