明めい暗あん境きょう界かい線せん

noun

terminator; twilight zone

Astronomical term for the dividing line between the illuminated and dark portions of a celestial body. Also called the twilight zone.

• 月つきの明めい暗あん境きょう界かい線せんは、クレーターの観かん察さつに適てきしている。

  The lunar terminator is suitable for observing craters.