What are those beams of light that emerge from clouds?

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What are those beams of light that emerge from clouds?
rays of light coming from behind cloud. Blue sky behind
Photo by William Gantz

Brilliant beams of light extending from clouds are often seen during the early morning or early evening. Called “crepuscular rays,” these occur during the crepuscular hours — around dusk and dawn.

A cloud between you and the sun can block some of its light, which produces those darker regions of the cloud. Where the light peeks through the object, scattering illuminates its path from the sun to your eyes, which creates beams in the sky. That’s because rays of light can change direction, or scatter, when they encounter small particles suspended in the atmosphere.

These beams appear to converge toward the sun; however, this is an illusion, similar to the impression that the railroad tracks appear to join in the distance. When crepuscular rays spread down to the ground, they are called Jacob’s Ladder, a “ladder to heaven.”

Mountains can generate crepuscular rays when they shadow the sun. You also can see this effect in buildings with tall ceilings when the sunlight shines directly through the windows, provided there is enough haze or dust particles in the building so that the sunlight will scatter toward you.
You can occasionally see beams of light converging on the opposite side of the sun, or the anti-solar point. These rays are called anti-crepuscular rays and are similar to crepuscular rays.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.