Sekstant

A sextant is an angle measuring instrument used to measure the angle between the visible horizon and a celestial body. This angle is called the altitude of the celestial body.
Measurements with the sextant are used, among other things, in astronomical navigation for geographical positioning. For example, a measurement of the elevation of the North Star or the elevation of the Sun at noon can be used to determine the observer's latitude by consulting tables in an almanac.

The instrument is used by navigators in sea and aviation, among other things, for positioning and is therefore designed in such a way that it can be held in the hand without a tripod.
The instrument consists of a frame of 60 degrees and is equipped with a scaled limbus (nonius) and a movable radial arm, the alidade with a mirror and a window with a reading mark on the limbus. Also attached to the frame are a fixed mirror, optical accessories and tinted glass to protect against sunlight.

The name derives from the Latin sextans, meaning one-sixth, since the instrument measures 60 degrees (or one-sixth of a full circle) and is an evolution of the octant (which was 45 degrees, or one-eighth of a full circle).

The nautical sextant with mirrors, believed to have come into use in 1767, is a further development of the octant and was believed to have been invented by the Englishman John Hadley in 1731. Around the same time, the American Thomas Godfrey made a similar invention. For astronomical use (without mirrors and telescopes) the sextant appeared as early as the 16th century.