Outside the umbral cone is that of the penumbra, within which the sun is partially hidden by the moon.
1590s, "phantom, ghost," a figurative use from Latin umbra "shade, shadow" (see umbrage). Astronomical sense of "shadow cast by the earth or moon during an eclipse" is first recorded 1670s. Meaning "an uninvited guest accompanying an invited one" is from 1690s.
Plural umbras or umbrae (ŭm'brē)