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Crepuscular rays, in atmospheric optics, are rays of sunlight that appear to radiate from a single point in the sky. These rays, which stream through gaps in clouds, are parallel columns of sunlit air separated by darker cloud-shadowed regions. The term "crepuscular" comes from their frequent occurrences during twilight, when the contrasts between light and dark are the most obvious. Various aerosols scatter the sunlight and make these rays visible. The reason we see the light so defined is because of diffraction, reflection and scattering. Crepuscular rays are near-parallel, but appear to diverge because of linear perspective. They often occur when objects such as mountain peaks or clouds partially shadow the sun's rays.

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