Crepuscular rays, sometimes colloquially known as god rays, twilight rays, or Jacob's ladder, are visible shafts of sunlight that originate when the Sun appears to be just above or below a layer of clouds, during the twilight period. Crepuscular rays are often observed as visible light beams passing through gaps in clouds, and are especially prominent when the contrast between light and dark is most obvious. The term "crepuscular" comes from the Latin word crepusculum, meaning "twilight".