Eclipses — Understanding the Penumbra In eclipse geometry, what is the Penumbra?

Introduction / Context:
During a solar eclipse, the Moon casts a shadow on Earth. That shadow has two main parts: the dark central core (umbra) and a lighter, outer region (penumbra). Knowing these terms helps explain why some locations see totality while others experience only a partial eclipse.

Given Data / Assumptions:

• We are discussing solar-eclipse shadow geometry.
• Umbra = region of total obscuration; penumbra = partial obscuration.
• Option phrasing uses simple language intended for school-level clarity.

Concept / Approach:
The penumbra is the outer portion of the shadow where the Sun is only partially blocked by the Moon. Observers inside the penumbra see a partial solar eclipse. Only observers within the much narrower umbral path see the Sun fully covered. The “tangent” wording in another option is not a standard definition and adds confusion.

Step-by-Step Solution:

Verification / Alternative check:
Diagrams in textbooks always label the broader, lighter ring as the penumbra; only the narrow dark cone is the umbra.

Why Other Options Are Wrong:

• “Formed by the tangent …” is vague and not a proper definition.
• “Both (a) and (b)” cannot be correct because (b) is not a correct definition.
• “None of the above” is false since (a) is correct.

Common Pitfalls:
Confusing penumbra with antumbra (annular eclipses). The penumbra pertains to partial eclipses, not the annular central zone.

Final Answer:
the outer portion of the moon's shadow