| The horizon should be clearly defined and the brightest stars should be visible under good atmospheric conditions i | |
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| In the beginning of morning astronomical twilight and at the end of astronomical twilight in the evening, sky illumination is very faint, and might be undetectable | One still should be able to carry on ordinary outdoor activities |
The time period when the sun is between 12 and 18 degrees below the horizon at either sunrise or sunset.
17.
8