Sextant
An instrument used for measuring angles primarily of celestial bodies like sun or a star...
by Manpreet

The sextant is an instrument used for measuring angles primarily of celestial bodies like sun or a star. It is also used in navigating ships and planes to determine the latitude.

The word sextant comes from the Latin word, "sextus" which means "one sixth". In fact the instrument is equipped with an arc which is usually one sixth of a circle or 60 degrees. It is shaped like the wedge of a pie, with a scale marked on its round edge.

The sextant was invented by a Englishman, John Hadley in 1731. It was mainly used at the sea to determine a ship’s latitude or distance from the equator. In fact, the invention of the sextant laid the foundation of modern navigation.

The device consists of an arc of a circle, marked off in degrees, and a movable radial arm pivoted at the center of the circle. A movable mirror is fixed at the end of the arm. The other end extends to the scale. A telescope is mounted on the sextant, and a glass mirror is mounted in front of the telescope.

To operate the sextant, the operator looks through the telescope straight at the horizon. And then moving the mirror the sun or any particular star made to appear exactly on the horizon. The arm, which moves the mirrors, gives the required measurement of the angle. From this angle and the exact time of day, the latitude is determined by means of published tables.

The knowledge of latitude is very useful for navigators as it tells them, at which place of the earth they are.