Navigate Using A Sextant
| Field | Navigation of a ship or airplane |
| Went Obsolete | Never |
| Made Obsolete By | LORAN navigation system, then GPS |
| Knowledge Assumed | For navigating with the sun: simple trigonometry. For navigating with stars: substantial training and practice |
| When useful | When your GPS breaks, when you're adrift in a lifeboat or all the time by the Royal Navy (or any other Navy) |
A sextant is a small handheld device, requiring no electrical power, that measures the angle between the sun (or other celestial body) and the horizon. This is useful in figuring out where you are, particularly if you're in the middle of an ocean, and need to decide which way to sail. The simplest case uses the sun: the height of the sun at noon tells you your latitude, and the time of local noon tells you your longitude (if you have an accurate timepiece). Simple trigonometric calculations are required.
If you have a book called an ephemeris, which tells you where various other celestial objects are scheduled to appear in the sky, you also navigate with stars and planets. But the calculations are significantly more complex.
They British Royal Navy do not use GPS for navigation within sight of land. Also all navigation officers regularly confirm GPS position using traditional navigation methods. GPS can not be relied upon in a time of war.
