Nautical Twilight ends when the Sun's geometric center is 12º below the horizon – that is the actual moment of
replica orologi Nautical Dusk and the beginning of Astronomical Twilight. Nautical Dusk and Dawn were, historically, the moments when military operations had to halt and defensive positions assumed, or when operations could commence, as those moments were when available light had fallen below the minimum needed to engage the enemy, or had increased to the point that maneuver was possible.