Sextant

A **sextant** is an instrument for **determining the angle between the horizon and a celestial body** such as the Sun, the Moon, or a star. By knowing this angle it is possible to determine **latitude and longitude**.



The device consists of an arc of a circle with scale in degrees, and a movable arm pivoted at the center of the circle. On this arm a mirror is placed. The telescope is important part, mounted rigidly to the framework. It is lined up with the horizon.



The radial arm has to be moved until the star is reflected into a half-silvered mirror in line with the telescope and appears, through the telescope, to coincide with the horizon. The angular distance of the star above the horizon is then read from the scale of the sextant.



One of the earliest precursors to the sextant was referred to as a **latitude hook**. This invention of the Polynesians could only be used to travel from one place at one latitude to another at the same latitude. The hook end of the device served as a frame for the North Star, a fixed celestial body also known as **Polaris**.