the dark part of a shadow where light from a source is completely blocked is called the
Umbra, penumbra and antumbra The umbra (Latin for "shadow") is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body. An observer in the umbra experiences a total eclipse. The umbra of a round body occluding a round light source forms a right circular cone; to a viewer at the cone's apex, the two bodies are equal in apparent size. The distance from the Moon to the apex of its umbra is roughly equal to that between the Moon and Earth (384,402 km (238,856 mi)). Since Earth's diameter is 3.70 times the Moon's, its umbra extends correspondingly farther: roughly 1,400,000 km (870,000 mi).[1]