Question

the lighter part of a shadow that surrounds the umbra eclipse solar eclipse lunar eclipse penumbra

Explanation:

The term "the lighter part of a shadow that surrounds the umbra" is a direct definition. Among the options, "penumbra" is the correct term for this description. "Eclipse" is a general phenomenon (like solar or lunar eclipse). "Solar eclipse" and "lunar eclipse" are specific types of eclipses, not related to the shadow part definition.

Answer:

penumbra