shadow

thumb|The shadow of a musician cast onto a brick wall thumb|Park fence shadow is distorted by an uneven snow surface. thumb|Shadows from cumulus clouds thick enough to block sunlight A shadow is a dark area on a surface where light from a light source is blocked by an object. In contrast, shade occupies the three-dimensional volume behind an object with light in front of it. The cross-section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.

== Point and non-point light sources == thumb|right|Umbra, penumbra and antumbra 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 two penumbras overlap, the shadows appear to attract and merge. This is known as the shadow blister effect.