Celestial Navigation · Twilight — Nautical Twilight
Nautical twilight is defined by the sun being:
- ABetween 6° and 12° below the celestial horizon✓ Correct
- BBetween 0° and 6° below the horizon
- CBetween 12° and 18° below the horizon
- DExactly on the horizon
Explanation
Civil twilight: sun 0°–6° below the horizon. Nautical twilight: 6°–12° below. Astronomical twilight: 12°–18° below. The Nautical Almanac tabulates the times of nautical and civil twilight by latitude for planning observations.
Authority: Nautical Almanac; Bowditch (Pub. No. 9), twilight
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