astronomical twilight

uncountable

The period in which the sun is between 12° and 18° below the horizon in the morning and evening.

Japanese Meaning

太陽が地平線下12°から18°の間に位置する、朝と夕の時間帯のこと。

Scientists scheduled their observations for astronomical twilight to ensure the sky was dark enough for faint object imaging.

科学者たちは、暗い天体の撮影に適するよう、太陽が地平線下12°から18°の間にある時間帯に観測を予定した。

Sense（1）

The period in which the sun is between 12° and 18° below the horizon in the morning and evening.