In astronomy, an umbra is the central, darkest part of a shadow cast by an object, such as during an eclipse. It is the region where the light source is completely blocked by the occluding object, leading to a total eclipse. For a solar eclipse, the umbra is the area where the Moon entirely covers the Sun, creating a total solar eclipse. Conversely, during a lunar eclipse, the Earth casts an umbra over the Moon, resulting in a total lunar eclipse. The umbra is contrasted with the penumbra, which is the outer part of the shadow where the light is partially obscured. Understanding the umbra helps astronomers predict and study the occurrences of eclipses.