dusk

Dusk is the period of twilight that follows sunset, during which the Sun is below the horizon but residual light keeps the sky visible. It marks the transition from day to night. Twilight is categorized by the Sun’s angle below the horizon: civil dusk (up to 6 degrees below), nautical dusk (6–12 degrees), and astronomical dusk (12–18 degrees). These stages reflect decreasing levels of natural illumination.

Duration and occurrence: Dusk duration varies with latitude and season. In temperate zones, civil dusk typically lasts about 20 to 40 minutes after sunset; nautical dusk may extend the twilight by another 20 minutes, and astronomical dusk by an additional 20 minutes. At higher latitudes, dusk can be prolonged in summer and brief or nearly absent in winter; in polar regions, twilight can persist for long periods during the midnight sun.

Atmosphere and color: The fading light is caused by the Sun’s rays scattering through the atmosphere; as the Sun sits lower, longer wavelengths dominate, producing reds and oranges near the horizon. Atmospheric conditions such as humidity, aerosols, and clouds influence color and visibility. A common phenomenon during dusk is the Belt of Venus, a pinkish or purple band above Earth's shadow just after sunset.

Uses and culture: Dusk is a common reference in photography and outdoor activities due to the soft light. Several regulatory definitions use dusk to indicate lighting requirements as daylight fades; culturally, dusk has various symbolic meanings in literature and art.