Civil twilight

Civil twilight is the period when the center of the Sun is between 0 and 6 degrees below the horizon. During it the brightest stars and planets show, the horizon stays clearly visible, and outdoor work proceeds without artificial light. At sea the navigator times star and planet sights for nautical twilight, when the Sun is 6 to 12 degrees down and both the horizon and the stars are seen together, rather than civil twilight when most stars are still washed out. The Nautical Almanac tabulates the times of civil and nautical twilight by latitude for planning the morning and evening sight rounds.