An Etymological Dictionary of Astronomy and Astrophysics

1. The portion of a shadow in which light from an extended source is partially but not completely cut off by an intervening body; the area of partial shadow surrounding the umbra.
   

2. The lighter part of a shadow during an eclipse. An observer standing in the penumbra of a Solar eclipse will see a partial eclipse.
   

3. The lighter zone surrounding the dark area (→ umbra) of a → sunspot. It consists of fine, light filaments which are approximately radial for sunspots with circular outline, but irregular for complex spots.

Etymology (EN): N.L., from L. pæne “almost” + → umbra “shadow.”

Etymology (PE): Nimsâyé, from nim “mid-, half” (Mid.Pers. nêm, nêmag “half;” Av. naēma- “half;” cf. Skt. néma- “half”)

• sâyé, → shadow; →umbra.