Science of directing a craft by determining its position, course, and distance traveled.
Early mariners followed landmarks visible on shore and studied prevailing winds for clues to direction. The Phoenicians and Polynesians sailed out of sight of land and used the stars to set their course. The compass (first used by the Chinese с 1100) was the first navigational aid that gave a constant reference point, though its accuracy was limited, especially in heavy seas. Modern compasses are stabilized by sextant and the astrolabe . Longitude (used for navigation with increasing success in the 17th–18th century) was fixed using {{link=chronometer">chronometers and tables showing positions of celestial bodies throughout the year. In the 20th century, radio beacons and satellite networks allowed aircraft and ships to determine their position. Dead reckoning uses an accurate history of a vessel's headings and speeds drawn from gyroscopes and from computerized measurements of the craft's acceleration. See also Global Positioning System .