Sextant

This precision navigation tool allows a skilled user to calculate his latitude. The basic purpose is to measure the height of a star or other heavenly object above the horizon. If a measurement of the sun’s height at noon is taken, then the measured angle relates directly to the latitude of the observer using the sextant. Skilled navigators can also use the moon or any star listed in a naval almanac for the same purpose. If a navigator uses his sextant horizontally, he can measure the angle between any two prominent landmarks and so, by triangulation, accurately fix his own position on a chart. This is a huge advance on any method of dead reckoning, even if it does not help in establishing longitude.
A sextant is a delicate thing and requires skilled repair if damaged.
Historically, the sextant was a development of earlier devices like the backstaff and the astrolabe. The sextant is so-called because the measuring arc is exactly one-sixth of a circle. Earlier attempts at similar instruments were the octant (one-eighth) and quadrant (one-quarter both used the same basic sighting method, but the arc was either too small to be practical or made the device unwieldy.

Item type

Navigational Aid / Instrument