航こう海かい薄はく明めい

noun

nautical twilight

Technical term in astronomy and navigation for the period when the sun is between 6 and 12 degrees below the horizon, providing enough light for sailors to take reliable star sights.

• 航こう海かい薄はく明めいの時じ間かん帯たいは、星ほしと水すい平へい線せんの両りょう方ほうが見みえるため、船ふな乗のりにとって重じゅう要ようです。

  The period of nautical twilight is important for sailors because both stars and the horizon are visible.