What are the two parts of a shadow?

The concept of a shadow is divided into two distinct regions: the umbra and the penumbra. The umbra is the area of complete shadow where the light source is entirely blocked by the object causing the shadow. This means that in the umbra, no direct light from the source reaches that part of the surface.

On the other hand, the penumbra is the area surrounding the umbra where the light is only partially obscured. In this region, some light from the source still reaches the observer, creating a gradient of shadow rather than a solid darkness.

Together, the umbra and the penumbra describe the full structure of a shadow cast by an object blocking light. Understanding both terms is essential in astronomy, especially in the context of eclipses, where the different parts of a shadow determine the visibility of celestial events. Hence, the answer combining both parts reflects the complete understanding of shadow formation.