A sextant is a navigational instrument used to measure the angle between two visible objects, typically the horizon and a celestial body like the Sun or a star. It helps sailors determine their latitude and longitude at sea, which is crucial for accurate navigation. The device consists of a graduated arc and a movable arm called an index arm. Invented in the 18th century, the sextant improved upon earlier tools like the astrolabe and the quadrant. It allows for precise measurements, enabling mariners to chart their course effectively. Despite modern technology, such as GPS, the sextant remains a valuable tool for traditional navigation.