I assume you're asking "what is" the dark part of a solar eclipse -- it's the moon. One of the more interesting coincidences of our solar system's makeup is the fact that the apparent diameter of the sun and the moon as seen from earth are identical. When there's a total solar eclipse, the moon exactly covers the sun.
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.
You will see a partial eclipse if you are in the penumbra.
During a total solar eclipse, the shadow is called the umbra. It is the darkest part of the shadow where the moon completely blocks the sun. The umbra creates the area on the Earth where a total eclipse can be seen.
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.
Umbral shadow refers to the darkest part of a shadow, where no direct light can reach. It is the region that is fully obscured from light sources, resulting in complete darkness.
the darkest part of the moon's shadow is called the 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 umbra is the darkest part of the shadow, the "complete shadow" area. We typically use the word "umbra" in reference to lunar eclipses, not solar eclipses.
The darkest part of the moon is called the Umbra. That is the darkest not the largest.
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.
penumbra
The penumbra
It is called the Umbra, the 'lighter' part of the shadow is the Pen-umbra
The shadow cast by the moon on Earth during a solar eclipse is called the umbra. This is the central, darkest part of the shadow. Surrounding the umbra is a lighter shadow called the penumbra, where only a partial eclipse is visible.
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.
You will see a partial eclipse if you are in the penumbra.
A partial solar eclipse will never be observed. This is because a partial solar eclipse occurs when the Moon covers only part of the Sun, resulting in a partial shadow being cast on Earth, but it is the darkest part of the shadow known as the umbra that creates a total solar eclipse.