A penumbra is a partially shaded area, in particular “that of the shadow cast by the moon on the earth in a solar eclipse, or by the earth on the moon in a lunar eclipse, resulting in an area that experiences only a partial eclipse” (OED). The word comes from Latin pen- (“almost”) and umbra (“shadow”); that pen- is the same “almost” we see in penultimate: the almost-last thing in a series.
But I’m not here to talk about astronomy or Latin or second-to-last things. I’m here to talk about abortion, the US Supreme Court, the US Constitution, and a thrilling theatrical performance I urge you to see.
Earth’s umbra (central shadow) and penumbra (extended shadow) during a lunar eclipse. Via NASA.gov.