Sunbeams: a Nice Light Show

Sunbeams 2I was admiring a beautiful light display the other day when the early morning sun went behind a small cloud, resulting in rays of sunlight appearing to shoot out from the cloud edge in all directions.  After decades of seeing sunbeams I wondered what caused them, and my researched answer is forthwith.

 

Sun rays or sunbeams are formed when columns of sunlight are separated out by darker cloud-shadowed regions of the sky.  Think of it as rays of sun that leak out of gaps in clouds or between other objects like mountains or even trees in the forest.   Airborne particles reflect the sunlight and make it visible as a beam.  The science guys call sun rays crepuscular rays, because they normally occur at dawn or dusk, known as crepuscular hours (twilight), when the contrast between light and dark are most obvious to the eye.

Sun rays are actually parallel to each other, but often appear to diverge in a fan pattern because of a phenomenon called linear perspective (I looked it up… very deep).

 

There are three main forms of crepuscular rays: rays of light that penetrate through holes in low clouds, beams of light diverging from behind a cloud, and rays that radiate from below the horizon.  The latter rays are often red or yellow in appearance because the atmosphere acts as a giant lens that refracts low sunset rays into long curving paths that pass through a lot of atmosphere.  This causes short wavelength blue and green light to be filtered out more than longer wavelength yellow and red.

 

Many names have been given to sunbeams.  There are profound names like God’s rays, or the fingers of God.  They have been referred to as a visible indication of  “the sun drawing water”, which I guess is technically correct, since the sun does cause evaporation.  Another name is “Jacob’s ladder”, a reference to the story in Genesis of Jacob and his vision of a ladder going up to heaven.  A native of Hawaii would call sunbeams “ropes of Maui”, from a folktale of Maui Potiki (a mythical hero) restraining the sun with ropes to make the days longer.  Whatever their name or cause, sunbeams are beautiful to gaze upon, so if you see them driving to work some morning, pause and enjoy them.

 

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