penumbra
the darkest part of the moon's shadow is called the umbra
The "umbra" is the dark area of complete shadow. Around it is the "penumbra", which is partial shadow.
The darkest part of the moon is called the Umbra. That is the darkest not the largest.
The penumbra
It is called the Umbra, the 'lighter' part of the shadow is the Pen-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.
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.
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.
"Umbra" means "shadow"; specifically the darkest part of the shadow of a planet or moon during an eclipse.