Twilight is the period of time just before sunrise and just after sunset when the sun is below the horizon but its light is scattered in the atmosphere, making the sky partially illuminated though the ground is still dark. It is the time between daylight and darkness. There are three types of twilight, defined by how far the sun is below the horizon:
- Civil twilight: Sun less than 6 degrees below horizon; usually bright enough for outdoor activities without artificial light.
- Nautical twilight: Sun between 6 and 12 degrees below horizon; general outlines visible but details less so.
- Astronomical twilight: Sun between 12 and 18 degrees below horizon; faintest light, sky mostly dark.
Twilight happens twice daily — in the morning before sunrise (dawn) and in the evening after sunset (dusk). Near the poles at certain times of the year, twilight can last all night without darkness. In short, twilight is when the sun is below the horizon but the sky is still lit up by its scattered light, marking the transition periods between day and night.
