During a solar eclipse, what is the darkest part of the moon’s shadow called
During a solar eclipse, the darkest part of the Moon's shadow is called the "umbra." When the Moon passes directly between Earth and the Sun, it casts two types of shadows on Earth: the umbra and the penumbra.
The umbra is the fully shaded inner region of a shadow where the light source (in this case, the Sun) is completely blocked by the occluding body (the Moon). Observers within the umbra experience a total solar eclipse, where the Sun's disk is entirely covered by the Moon, and it can get very dark, much like nighttime.
Outside of the umbra but still within the Moon's shadow lies the penumbra, the shadow's partial or lighter outer part. Observers in the penumbra experience a partial solar eclipse, where only a portion of the Sun's disk is obscured.
There's also a third type of shadow cast during an annular eclipse called the antumbra, which is beyond the umbra. In an annular eclipse, the Moon is too far from Earth to completely cover the Sun's disk, and viewers in the antumbra see what is called a "ring of fire" or an annulus where a thin, bright ring of the Sun's surface surrounds the Moon.