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ASA 117 Basic Celestial Navigation Endorsement

Basic Celestial Navigation Endorsement

Learn to apply basic celestial navigation theory and practice to determine latitude and longitude at sea using a sextant and Nautical Almanac.


  • Basic math skills


  • Describe the terms and theory of Basic Celestial Navigation.
  • Using a traditional sextant and Nautical Almanac and without the use of a programmed calculator or computer
  • Convert between standard time and zone time to GMT/UT in either direction.
  • Calculate the zone time at a given longitude.
  • Determine the times of sunrise, sunset and civil twilight for a vessel’s position.
  • Describe and identify the parts, principals and operation of a traditional sextant.
  • Determine altitudes of the Sun and Polaris by a traditional sextant.
  • Obtain Latitude and Longitude at noon (LAN) by applying the sextant corrections for conversions of the raw sextant altitudes (hs) of the Sun to the true celestial altitudes (HO) of the Sun.
  • Determine the vessel’s latitude and Estimated Position at morning and evening twilight by means of the altitude of Polaris.
  • Plot latitudes and EPs on a chart.


All course materials provided.

Duration 2 days

(rev 2022-12-14 A)