Shadow

Shadow is the darkness that an object causes when it prevents light from shining on a surface. When you stand in sunlight, your body blocks some of the light that would have otherwise brightened the ground. Thus, your shadow is a dark area in the shape of your body. The earth casts a shadow in space, because it blocks some of the light from the sun. The moon darkens during a lunar eclipse when it moves into the earth's shadow.

A shadow falls from the side of an object opposite the light source. If the light source is smaller than the object, the shadow is evenly dark. A wide source of light creates a shadow with a dark center called the umbra. The umbra is surrounded by a lighter region called the penumbra. The umbra is dark because the object blocks all the light directed toward that part of the surface. The penumbra appears when some of the light gets past the object and reaches the surface.

In bright sunlight, objects have dark, crisp shadows. On cloudy or hazy days, shadows are fainter. On such days, the sunlight is dimmer and particles in the air scatter some of the light into the shadows, brightening them.

Contributor: Jearl Walker, Ph.D., Prof. of Physics, Cleveland State Univ.

Shadow

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