noun, noun which may take the genitive case particle 'no'
Astronomical term for the partially shaded outer region of a shadow, especially during an eclipse. Also used as a no-adjective.
月食では、半影に入った部分が少し暗く見える。
During a lunar eclipse, the part that enters the penumbra looks slightly darker.
半影月食は肉眼ではわかりにくい。
A penumbral lunar eclipse is hard to notice with the naked eye.