Nightfall is the time of day when darkness arrives and night begins. It's that gradual moment when the sun slips below the horizon and the sky shifts from blue to deep purple to black. During nightfall, streetlights flicker on, stars begin to appear, and the world transitions from day to night.

The word captures something specific: not the middle of the night or the early evening, but that particular threshold when day ends. A hiker might hurry to reach camp before nightfall. A town's curfew might say children should be home by nightfall. In stories, nightfall often marks a turning point: the moment when nocturnal creatures emerge, when temperatures drop, or when visibility becomes limited.

Nightfall happens at different times throughout the year. In summer it might arrive at 9 p.m., while in winter it comes as early as 5 p.m. The exact moment varies by location too: places closer to Earth's poles experience extremely late nightfall in summer and extremely early nightfall in winter, while locations near the equator see nightfall at roughly the same time year-round.