How many letters does the top answer for “a bright spot on the parhelic circle; caused by diffraction by ice crystals” have?

The most common answer is parhelion (9 letters).

Crossword clue: a bright spot on the parhelic circle; caused by diffraction by ice crystals

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

parhelion 9 letters wn-def

a bright spot on the parhelic circle; caused by diffraction by ice crystals

sundog 6 letters wn-def

a bright spot on the parhelic circle; caused by diffraction by ice crystals