Question

why umbra darker than penumbra

Answer 1

Within the Moon's penumbra, only part of the Sun's disk is obscured. This means that the penumbra has a considerably lighter shade than theumbra, where the Sun is completely covered. However, the penumbralshadow's light level is not uniform. It is much darker in the areas adjacent to the umbra than at the edges.

Answer 2

Answer:

It is much darker in the areas adjacent to the umbra than at the edges. This variation is caused by the changing magnitude of the eclipse in different areas within the penumbra. In the penumbra's most central regions, just outside the umbra, the Sun appears nearly completely obscured.