Twilight is the period before sunrise and after sunset when the Sun is below the horizon but its light is still scattered through Earth’s atmosphere. This scattering bends sunlight around the planet, illuminating the sky even when the Sun itself is no longer visible. Twilight is divided into three main types, civil, nautical, and astronomical, based on how far below the horizon the Sun is, and each represents a distinct stage in the transition from day to night.

Civil twilight occurs when the Sun is between 0° and 6° below the horizon. During this phase, there is still enough natural light for most outdoor activities without artificial lighting. The sky often displays vivid reds, oranges, and pinks near the horizon, including the Belt of Venus, a soft pink band visible opposite the Sun caused by Earth’s shadow rising into the atmosphere, while the brightest stars and planets begin to appear. Civil twilight is commonly associated with the everyday concepts of dawn and dusk and is widely used in photography, aviation, and urban lighting schedules.

Nautical twilight takes place when the Sun is between 6° and 12° below the horizon. The sky darkens significantly, shifting toward deeper blues, while the horizon line remains faintly visible. This stage was historically important for sailors, who could use stars for navigation while still seeing the sea horizon for orientation. On land, most activities now require artificial lighting, and many more stars become visible.

Astronomical twilight occurs when the Sun is between 12° and 18° below the horizon. During this final stage, scattered sunlight fades almost completely, allowing faint stars, galaxies, and other deep sky objects to emerge. Astronomers define true night as beginning only after astronomical twilight ends, when the Sun is more than 18° below the horizon and the sky reaches its maximum darkness.

The duration of twilight varies with latitude and season. Near the equator, twilight is relatively brief because the Sun rises and sets steeply. At higher latitudes, twilight can last much longer, and in polar regions it may persist for hours or even all night during certain times of the year. These extended twilight periods help explain phenomena such as the midnight Sun and the prolonged darkness of polar winters.

Clear Skies,

Scott