Dusk

Dusk is the darkest stage of twilight, the very end of astronomical twilight after sunset and just before full night, and is distinct from both sunset, the moment the sun disappears below the horizon, and evening more generally. Like dawn, it is divided by how far the sun sits below the horizon into civil dusk at 6 degrees, where artificial light becomes needed to read outdoors, nautical dusk at 12 degrees, and astronomical dusk at 18 degrees, when the sky is dark enough for astronomical observation. Its length varies with latitude and season, lasting longest at high latitudes in summer and shortest near the tropics, where the sun drops toward the horizon at a steeper angle.