Celestial navigation glossary
Nautical twilight
Sun 12° below the horizon: the horizon is too dark for sights.
Where the course teaches it
Twilight: the window for star sights, in the module Planning a twilight fix. Find the time of twilight by your watch, and choose stars that give a good fix.
Taught alongside it
- Civil twilight
- Sun 6° below the horizon: bright stars visible and the horizon still sharp. The time for star sights.
- Local mean time (LMT)
- Time by the mean Sun at your meridian; the almanac lists sunrise and twilight in LMT.
- Star finder
- A star base and latitude templates (the 2102-D, or the Admiralty’s NP 323) that show every navigational star’s altitude and bearing for a given LHA of Aries.