A vocabulary of landscape — a landscape of words
1469 entries
halo
A halo is a ring or arc of light produced when sunlight or moonlight passes through ice crystals high in the atmosphere. The commonest is the 22-degree circle around the sun or moon, made by light refracting through six-sided column crystals, which always bends by at least that angle and so piles up light at that radius. Halos come in a family of dozens: sundogs, arcs, pillars, and rarer forms that appear a few times in a lifetime.
Etymology
The word is Greek and originally meant a threshing floor, which was a circular area of beaten earth where oxen walked round and round to tread out the grain. The circle they wore into the ground gave the Greeks their word for any disc or ring, including the one around the sun. The religious sense, the ring of light around a saint’s head in painting, came later and comes from the same source.
Notes
A halo is a genuine forecast rather than folklore. The ice crystals producing it sit in high cirrus, and cirrus commonly runs ahead of a warm front by a day or so, which is what the old rhyme about a ring around the moon meaning rain is conveying.