Celestial Navigation · Twilight — Local Time of Twilight
The Nautical Almanac tabulates twilight in LMT for the Greenwich meridian. To get the local zone time of twilight at your longitude you must:
- AUse the GMT directly with no correction
- BApply the arc-to-time longitude correction and the zone description (interpolating for latitude)✓ Correct
- CAdd the equation of time only
- DSubtract the dip correction
Explanation
Twilight is tabulated as LMT by latitude. Interpolate for your latitude, convert your longitude to time and apply it to get GMT, then apply the zone description to obtain local zone time — telling the navigator when to be on deck for the star round.
Authority: Nautical Almanac, twilight tables; Bowditch (Pub. No. 9)
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