Navigation is the art and science of directing a vessel from one place to another. Originally navigation applied only to marine vessels, but now air navigation and, increasingly, space navigation are also important. Although the techniques and applications of navigation have radically changed through time, the basic problem, and hence the principles, have remained much the same.
Primitive sailors could not venture out of sight of land without the risk of getting lost. But soon they learned to use sunset and sunrise, the prevailing winds, the pole star, and so forth as aids to direction. Early on, the first fathometer, a weighted rope used to measure depth, was developed. Before the a0th century AD the magnetic compass had appeared. But it was not until the 1730s that the invention of the sextant and chronometer heralded the dawn of accurate sea navigation. Both latitude and longitude could now be determined within reasonable tolerances.
Modern navigation uses electronic aids such as LORAN and the radiocompass; celestial navigation, the determination of position by sightings of celestial bodies, and dead reckoning where, by knowing one's position at a particular past time, the time that has elapsed since, and one's direction and speed, one can tell one's present position.
Air navigation uses many of the principles of marine navigation. In addition, the pilot must work in a third dimension, must know his altitude, and in bad weather must use aids the instrument landing system. Radar is also used.
Like air navigation, space navigation works in three dimensions, but the problems are exacerbated by the motions both of one's source (the Earth) and one's destination, as well as by the distances involved.