Revision as of 11:29, 16 October 2015

Navigating with a Sextant

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)
• Mechanical clock set to local time
• Celestial Sight Reduction Tables for Marine Navigation tables

Sun Shot at Local Apparent 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
• 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.

References

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