penumbra
noun [ C or U ] physics specialized uk/pɪˈnʌm.brə/ us/pɪˈnʌm.brə/
（日食、月食等的）半影
the part of a shadow, especially one made by something blocking the sun, in which only part of the light is blocked
In a lunar eclipse, the outer shadow or penumbra is a zone where Earth blocks a portion of the sun's rays. 月食发生时，外侧的暗影或称半影是地球把部分太阳光挡住了的区域。