penumbras

A penumbra is the partially shaded outer region of a shadow that is cast by an opaque object. It is the area where the light source is only partially blocked by the object. In contrast, the umbra is the region of complete shadow where the light source is entirely blocked. The penumbra is a common phenomenon observed during eclipses, such as solar eclipses, where the Moon passes between the Sun and Earth, and lunar eclipses, where the Earth passes between the Sun and Moon. During a solar eclipse, observers within the penumbra will see a partial eclipse, while those in the umbra will experience a total eclipse. Similarly, during a lunar eclipse, the Moon will appear to dim and redden as it passes through Earth's penumbra before entering its umbra. The size and shape of a penumbra depend on the relative sizes of the light source and the object casting the shadow, as well as the distance between them. The concept of a penumbra is also relevant in astronomy, particularly when discussing the shadows cast by celestial bodies.