SextantNavigation

Navigating with a Sextant

Discussion/Comments

In the event of an emergency when you lose your navigational electronics it would be useful to know how to navigate using a sextant. The simplest calculation is when you take a sun shot at local apparent noon (LAN).[1] [2]

Tools

Sun Shot at Local Apparent Noon

Use the sextant to track the sun angle to determine its maximum zenith, which is local noon.

Latitude

To determine latitude:

  • Point the sextant at the horizon
  • Look through the tekescope
  • Adjust the index mirror with the index bar until the Sun aligns with the horizon
  • Read the angle from the arc
  • Note the exact time
  • Consult a celestial table to calculate the latitude

Longitude

To determine longitude using a chronometer at local noon:[3]

  • Note the precise time of noon GMT
  • Know the local noon time at this moment
  • If local noon is before GMT noon you are on eastern logitutde
  • If local noon is after GMT noon you are on western logitutde

Each difference of 4 minutes = 1 degree longitude

Other Sightings

Other sightings of the sun (not at noon), moon or stars are complex and beyond the scope of this article. See also LearnToNavigate.

References

  1. http://www.navigation-spreadsheets.com/noon_shots.html
  2. http://celestialnavigation.net/practice/
  3. https://en.wikipedia.org/wiki/Longitude_by_chronometer