The Penumbra isthe outer portion of the moon's shadowformed by the tangent that intersects between the sun and the moonboth (a) and (b)None of the above

The question seems to ask about the definition of "Penumbra" in the context of lunar or solar eclipses. The penumbra is indeed the outer portion of a shadow cast by an object, where the light is partially obscured. This occurs when the sun, moon, and Earth are aligned, but not in a straight line, allowing some light to reach the area.

To clarify the options provided:

• (a) The penumbra is formed by the tangent that intersects between the sun and the moon.
• (b) It's likely that the options are not fully provided, but if considering shadows in eclipse phenomena, both statements might reference different aspects of the penumbra.

In this case, if the question is meant to evaluate understanding of these terms, the answer would depend on what (b) states. However, if (a) is accurately describing the penumbra, then (a) could be considered the correct choice.

To conclude, the penumbra is indeed the outer part of the shadow, and if (a) accurately describes that relationship, then it could be seen as correct depending on the context of (b). If there's additional information in (b) that contradicts this, that will further dictate the answer.