"Nightfall" is a science fiction short story by Isaac Asimov that explores the impact of darkness on a planet called Lagash. On this world, daylight lasts for long periods, and the inhabitants have never experienced true darkness. As the story unfolds, a rare astronomical event causes the sun to set, plunging the planet into night for the first time in thousands of years. The sudden arrival of darkness leads to chaos and fear among the people of Lagash. They confront their deepest fears and the unknown, revealing how fragile their civilization is when faced with a fundamental change. The story raises questions about human nature and the fear of the unknown.