Shadows are formed when light travelling in a straight line from a light source meets an object. The object blocks the light and a shadow is produced in the area behind the object. Shadows vary in quality and size. Objects that are solid block the light produce distinct shadows whereas those that let some light through have shadows that are less distinct.. The overall shape of a shadow corresponds to that of the object casting the shadow as can be seen in the image.

Shadows cast by the Sun have two parts: an umbra and a penumbra. The umbra is the area of total shadow where an object blocks all of the light from the Sun, whereas the penumbra is the area in partial shade around the edge of the shadow. Shadows are experienced in both solar eclipses and lunar eclipses.

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