In a shadow, the darkest central region where all light from the source is completely blocked is called the:

The umbra is the darkest, central part of a shadow, where the light source is completely blocked by the object casting the shadow. The word "umbra" is Latin for "shadow".

Parts of a shadow:

Umbra: the fully dark inner region. An observer in the umbra cannot see any part of the light source.

Penumbra: the lighter, outer region around the umbra. Here, only part of the light source is blocked, so the shadow is partial.

Antumbra: the region beyond the tip of the umbra, where the object appears smaller than the light source. An observer here sees a bright ring of the light source around the object.

Why shadows have these parts:

• If the light source were a single point, the shadow would have sharp edges and only an umbra.
• Because large sources like the Sun are extended (they have size), light from different parts of the source reaches the edges of the shadow, forming the penumbra.

Umbra and penumbra in eclipses:

• In a solar eclipse, the Moon casts its shadow on the Earth.
• People in the umbra see the Sun completely covered.
• People in the penumbra see the Sun only partly covered (a partial eclipse).

People in the antumbra see an annular eclipse, in which a bright ring of the Sun surrounds the Moon. This happens when the Moon is farther from the Earth and appears too small to cover the Sun completely.

In a lunar eclipse, the Earth's shadow falls on the Moon.

When the Moon passes through the Earth's umbra, the eclipse is total or partial.

When it passes only through the penumbra, the eclipse is penumbral and is hard to notice.

Why not the other options?

• ✗Penumbra is the partial, lighter outer shadow.
• ✗Antumbra is the region beyond the end of the umbra.
• ✗Corona is the outer atmosphere of the Sun, not a part of a shadow.