A long-lasting multiple halo display pictured by Maciej Mucha. A remarkable feature was the double halo just below the circumzenithal arc, CZA. Earlier in the day when the sun was higher it was single and there was no CZA.?
46 degree halos and supralateral arcs.
The two halos are a 46� halo, 46H, and a supralateral arc, SLA. The latter, and the CZA, only form when the sun is less than 32� high. The sun was slightly lower than this limit in the image above.?The 46H and SLA form from identical ray paths through hexagonal ice prisms. Their rays pass between a prism side face and an end face. Why then are the two halos different? The answer is in crystal orientation. SLAs are formed by prisms drifting with their long axes horizontal. 46Hs come from crystals (probably clusters) where the prisms are nearly randomly tilted.?Contrary to popular lore, the 46H is relatively rare and many sightings are actually SLAs. The 46H is more pastel coloured than the SLA. More on telling them apart here.??
46� halos and supralateral arcs as the sun gets higher. At 5� they are well separated at their tops. The SLA always touches the CZA. Let the sun reach 15� and they are almost merged. They only separate again with the sun higher than ~27�. Then, at 32� the SLA disappears.?