Twilight
Also called: civil twilight, nautical twilight, astronomical twilight, astronomical night, darkness.
The glow after sunset and before sunrise, in three stages: civil, nautical and astronomical.
Civil twilight lasts until the Sun is 6° below the horizon: bright planets appear. Nautical twilight lasts to −12°: the horizon fades and the brighter stars are out. Astronomical twilight lasts to −18°: the sky is nearly dark, but faint galaxies still suffer. Below −18° it's astronomical night — as dark as it gets.
Far from the equator in summer, the Sun never gets 18° below the horizon, and the whole night is twilight.
In AstroPilot
Tonight shows when real darkness starts and ends; the night strip shades the twilight stages.