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

• Sextant
• Mechanical clock set to Greenwich Mean Time (GMT)
• Some means of determining noon
• Celestial Sight Reduction Tables for Marine Navigation tables

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