The umbra, the penumbra and the antumbra are three different parts of a shadow, created by any light source after hitting an opaque object. Assuming no diffraction "Diffraction (physics)"), for a collimated beam (such as a point source) of light, only the umbra is projected.

These names are most often used for shadows cast by celestial bodies, although they are sometimes used to describe levels, as in sunspots.

The umbra (Latin for "shadow") is the deepest, darkest part of a shadow, where the light source is completely blocked by the occlusive body. An observer in the umbra experiences a total eclipse. The umbra of a round body occluding a round light source forms a right circular cone "Cone (geometry)"); to a viewer at the apex "Apex (geometry)") of the cone, the two bodies have the same apparent size. The distance from the Moon to the apex of its umbra is approximately equal to that between the Moon and Earth (384,402 km (238,856 mi)). Since the Earth's diameter is 3.70 times that of the Moon, its umbra extends correspondingly further: approximately 1,400,000 km (870,000 mi).[1]​.

The penumbra (from Latin paene, "almost" and umbra, "shadow") is the region in which only part of the light source is obscured by the occlusive body. An observer in the twilight experiences a partial eclipse. An alternative definition is that the penumbra is the region where part or all of the light source is obscured (i.e., the umbra is a subset of the penumbra). For example, NASA's Navigation and Information Facility defines that a body in the umbra is also within the penumbra.[2]​.

The antumbra (from Latin ante, "before" and umbra, "shadow") is the region from which the occlusive body appears completely within the disk of the light source. An observer in this region experiences an annular eclipse, in which a bright ring is seen around the eclipsing body. If the observer approaches the light source, the apparent size of the occlusive body increases until it causes a complete umbra.[3]​.

• - Anti-solar point.

• - Shadow of the Earth.