:This article's about the Sextant as used for navigation. For the astronomer's sextant, see Sextant (astronomical). » For the history and development of the sextant see Reflecting instruments A sextant's an instrument generally used to measure the altitude of a celestial object above the horizon. Making this measurement's known as sighting the object, shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or ae… (More on Sextant)