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]

Tools

• Sextant
• Mechanical clock set to Greenwich Mean Time (GMT)
• Mechanical clock set to local time
• Celestial Sight Reduction Tables for Marine Navigation tables

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:

• Note the precise time of noon GMT
• Know the local noon time
• If local noon is before GMT noon you asre on eastern logitutde
• If local noon is after GMT noon you asre on western logitutde

Each difference of 4 minutes = 1 degree longitude

1. ↑ http://www.navigation-spreadsheets.com/noon_shots.html