Methods

Astronomical Navigation

Astronomical navigation is among the first advanced methods of navigation other than primitive dead-reckoning (See below). Finding latitude at sea was relatively simple. It involved finding the altitudes of various stars (most often the north star or the sun) and simply taking a reading from an astronomical instrument. The most common ones were the quadrant and astrolabe (See Instruments). Finding longitude was more complicated. After observations and calculations, the distances between the moon and other stars could be predicted accurately. Sailors took onboard a chart of these distances. Sailors measured the distance between the moon and other stars and looked it up in their reference charts, giving them the GMT(Greenwhich Mean Time) of the observation. When compared with their local time, longitude can be determined with reasonable accuracy. Later, accurate clocks, or chronometers, replaced astronomical methods in determining longitude.

Radio

One of the earliest radio methods was the land-based transmitter. Land-based radio transmiters sent signals to ships at sea, allowing them to mark their position. Three transmitters send a ship transmissions and differences in arrival time can be calculated. From these arrival times can be calculated two hyperbolas (a kind of curve, or conic section). The ship could be located at an intersection of the two hyperbolas. Also, satellite navigation has made its debut recently. the GPS(Global Positioning System) and its NAVSTAR satellites are available to civilians with the right devices.

Dead-Reckoning

Dead reckoning is a method which the ship's starting location is known. As the ship moves, its movements relative to its previous locations are known and therefore its exact location can be known. In ancient times, dead recknoning was the only method. Sailors simply observed the ship's movements and estimated its location as accurately as possible. With computer aided methods, dead-reckoning is relatively accurate and can be adjusted by satellite. Accelerometers measure the acceleration of the craft, stabilized by gyroscopes(See Instruments). Dead-reckoning is of great importance because it, unlike other methods, functions completely independently of the outside environment and its versatility makes it vital.