What I know about dawn and dusk
da Bradley Darling
1. Twlight
1.1. "occurs when Earth's upper atmosphere scatters and reflects sunlight which illuminates the lower atmosphere." says Twilight, Dawn, and Dusk
1.2. Civil Twilight
1.2.1. occurs when the Sun is less than 6 degrees below the horizon. In the morning, civil twilight begins when the Sun is 6 degrees below the horizon and ends at sunrise. In the evening, it begins at sunset and ends when the Sun reaches 6 degrees below the horizon.
1.3. Nautical Twilight
1.3.1. occurs when the geometrical center of the Sun is between 6 degrees and 12 degrees below the horizon. This twilight period is less bright than civil twilight and artificial light is generally required for outdoor activities.
1.4. Astronomical Twilight
1.4.1. occurs when the Sun is between 12 degrees and 18 degrees below the horizon.