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Shadow facts for kids

Kids Encyclopedia Facts
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Shadow of a cactus on a wall
Looking down from The Eiffel Tower, Paris 8 April 2007
Shadows of visitors to the Eiffel Tower, viewed from the first platform

A shadow is a dark area on a bright surface. It is caused by something blocking a source of light. A shadow's outline, called a silhouette, will have the same shape as the object blocking the light.

Depending on the light source, or sources, a wide range of effects can be produced.

A point source of light casts only a simple shadow, called an "umbra". A "penumbra" is the region in which only a portion of the light source may be blocked. If there is more than one light source, there will be several shadows, with the overlapping parts darker, and various combinations of brightness or even colors.

The more diffuse the lighting is, the softer and more indistinct the shadow outlines become, until they disappear. The lighting of an overcast sky produces few visible shadows,

Astronomical shadows are usually sharp. This is because in space the light usually does not go through an atmosphere.

Point and non-point light sources

A point source of light casts only a simple shadow, called an "umbra". For a non-point or "extended" source of light, the shadow is divided into the umbra, penumbra and antumbra.

The wider the light source, the more blurred the shadow becomes.

If there is more than one light source, there will be several shadows, with the overlapping parts darker, and various combinations of brightnesses or even colors.

The more diffuse the lighting is, the softer and more indistinct the shadow outlines become, until they disappear. The lighting of an overcast sky produces few visible shadows.

Astronomy

Three moons and their shadows parade across Jupiter
Three moons (Callisto, Europa and Io) and their shadows parade across Jupiter.

The names umbra, penumbra and antumbra are often used for the shadows cast by astronomical objects, though they are sometimes used to describe levels of darkness, such as in sunspots.

The only astronomical objects able to project visible shadows onto Earth are the Sun, the Moon, and in the right conditions, Venus or Jupiter.

Night is caused by the hemisphere of a planet facing its orbital star blocking its sunlight.

A shadow cast by the Earth onto the Moon is a lunar eclipse. A shadow cast by the Moon onto the Earth is a solar eclipse.

Daytime variation

The sun casts shadows which change dramatically through the day. The length of a shadow cast on the ground is depends on the sun's elevation angle relative to the horizon.

Near sunrise and sunset when the sun is very close to the horizon, shadows can be extremely long. If the sun is directly overhead, the shadows are cast directly underneath objects and appear very small.

These things have aided travellers during their travels, especially in barren regions such as the Arabian Desert.

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