Shadow
Shadow (disambiguation).
A shadow is a dark shape, e.g. on the ground or a wall, caused by an object (or person, etc.) blocking light. Like a silhouette, the shape of the shadow is a two-dimensional projection of the object, but:
- the smaller the angle between an elongated object and the direction of the light is, the shorter the shadow is;
- the smaller the angle between the direction of the light and the surface on which the shadow occurs is, the longer the shadow is;
- if the object is close to the light source, the shadow is large.
If the surface is curved there are further distortions.
For non-point sources of light, the shadow is divided into the umbra and penumbra. The wider the light source, the more blurred the shadow.
If there are multiple light sources there are multiple shadows, with overlapping parts darker. For a person or object touching the surface, like a person standing on the ground, or a pole in the ground, these converge at the point of touch.
If white light is produced by separate colored light sources, the shadows are colored.
A shadow cast by the Earth on the Moon is a lunar eclipse. Conversely, a shadow cast by the Moon on the Earth is a solar eclipse.
More generally the term shadow is also used with regard to other things than light, for example rain: a rain shadow is a dry area, which, with respect to the prevailing wind direction, is beyond a mountain range; it is dry because air masses lose part of their water when they move over these mountains.
Fiction: In Peter Pan the main character loses his shadow: it snaps off when he leaps out of the window, which is slammed closed behind him. It is put in a drawer and later sewed back on by Wendy.
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