Twilight's the time between dawn and sunrise, and the time between sunset and dusk. Sunlight scattered in the upper atmosphere illuminates the lower atmosphere, and the surface of the Earth's neither completely lit nor completely dark. The sun itself isn't actually visible because it's below the horizon. Due to the unusual, romantic quality of the ambient light at this time, twilight has long been popular with photographers and painters, who refer to it as the "blue hour" or "sweet light", afte… (More on Twilight)