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What are crepuscular rays?

Published On: Jul 27 2011 12:14:52 PM CDT

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 or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions.

The name comes from their frequent occurrences during crepuscular hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious.

Crepuscular rays are near-parallel, but appear to diverge because of linear perspective.

Think of crepuscular rays as a set of railroad tracks.

When you view railroad tracks straight-on, you may note that they appear to converge at a point in the distance, even though this is not the case.

Crepuscular rays work in the same way.

They often occur when objects such as mountain peaks or clouds partially shadow the sun's rays like a cloud cover.

Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction, reflection, and scattering.

Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in the ice.

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