the darkest part of the moon's shadow is called the umbra
The darkest part of the moon is called the Umbra. That is the darkest not the largest.
penumbra
The penumbra
It is called the Umbra, the 'lighter' part of the shadow is the Pen-umbra
I think you are asking what is the lighter part of the Earth's shadow on the Moon that surrounds the darkest part. The penumbra is this lighter part of the shadow. The darkest part is the umbra.
umbra
There are two parts of a shadow: the UMBRA and the PENUMBRA. UMBRA is the inner darker part of a shadow. PENUBMRA is the outher lighter layer of a shadow. During a solar eclipse, the area on the planet that witnesses a complete total solar eclipse would be under the moon's shadow's UMBRA. The area that views a partial solar eclipse would be under the PENUMBRAL shadow.
The penumbra.
A complete area of shadow is called an umbra. It is the darkest part of a shadow where no light reaches.
When you are in the moon's shadow during a solar eclipse, it is called the umbra. This is the central, darkest part of the shadow where the sun is completely blocked by the moon. Outside of the umbra is the penumbra, where the sun is only partially blocked, resulting in a partial eclipse.
During a total solar eclipse, the umbra or darkest part of the moon's shadow creates darkness on a small section of the Earth's surface. The penumbra is a part of the moons shadow that is more wide spread and not nearly as dark.
The darkest part of a shadow is called the "umbra" The lighter part of a shadow is called the "penumbra" An "antumbra" is the area of light which surrounds the object creating a shadow, as in a "ring of fire" eclipse (like the recent one in May, 2012). It can best be seen when the viewer is beyond the focal point of the umbra, but in line with it.