Twilights, evening and morning, are that time span when the Sun is below the horizon, yet it still lights up the sky. By convention there are three types of twilight: civil twilight begins when the Sun sets and ends when it is six degrees below the horizon; nautical twilight begins when civil twilight ends and finishes when the Sun is twelve degrees below; while astronomical twilight begins when nautical twilight ends and ends when the Sun is eighteen degrees below the horizon. The latter marks the start of astronomical night. The three twilights last a total of 18 degrees (6 degrees each). During sunset and the following twilight the sky changes color rapidly, so that many phenomena can be observed, including: the purple light with the Sun between -4 and -6 degrees below the horizon, the Earth's shadow cone with the Sun between -2 and -6 degrees, and the Enrosadira with the Sun between -6 and -8 degrees below the horizon, and the zodiacal light visible at the start of astronomical night.
The colors of twilight
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