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Crepuscular rays
Crepuscular rays (also known as sunbeams, Sun rays or God rays), in atmospheric optics, are rays of sunlight that appear to radiate from the point in the sky where the sun is located. These rays, which stream through gaps in clouds (particularly stratocumulus) or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions. Despite seeming to converge at a point, the rays are in fact near-parallel shafts of sunlight, and their apparent convergence is a perspective effect (similar, for example, to the way that parallel railway lines seem to converge at a point in the distance).
The name comes from their frequent occurrences during twilight hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious. Crepuscular comes from the Latin word "crepusculum", meaning twilight.
==Anticrepuscular rays==
(詳細はantisolar point, the point on the sky sphere directly opposite the sun. In this case they are called ''anticrepuscular'' or ''antisolar rays''. These are not as easily spotted as crepuscular rays. This apparent dual convergence (to both the solar and antisolar points) is a perspective effect analogous to railway tracks appearing to converge to opposite points in opposite directions.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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