Here's why:

* Penumbra: This is the outer, less dark region of a shadow where the light source is only partially blocked. During an eclipse, the penumbra receives some light from the Sun, making it lighter than the umbra.

* Umbra: This is the inner, darkest region of a shadow where the light source is completely blocked. During an eclipse, the umbra receives no direct sunlight.

So, during a solar eclipse, the penumbra is the region where you experience a partial eclipse, while the umbra is where you experience a total eclipse.