Celestial Navigation · Twilight
Civil twilight is defined as the period when the Sun's center is:
- AExactly on the visible horizon
- BBetween 6° and 12° below the horizon
- CBetween 0° and 6° below the horizon✓ Correct
- DMore than 18° below the horizon
Explanation
Civil twilight is from sunset until the Sun is 6° below the horizon (and the reverse at dawn). Nautical twilight extends to 12° below, and astronomical twilight to 18°. The Almanac tabulates the times of civil and nautical twilight.
Authority: Bowditch (Pub. No. 9)
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