An Etymological Dictionary of Astronomy and Astrophysics

Rays of sunlight that appear to diverge from a single point in the sky when parallel columns of light, partially blocked by clouds, pour through gaps in clouds. They result from
light scattering and an optical effect called perspective.

Etymology (EN): Crepuscular “of, pertaining to, or resembling twilight,” from L. crepuscul(um), “twilight, dusk,” from crepus-, from creper “dusky, dark.”

Etymology (PE): Partowhâ “rays,” from partow, → ray; nimtâbi “of, pertaining to, or resembling nimtâb” → twilight.