Celestial navigation, is a position fixing technique that was devised to help sailors cross the worlds oceans without having to rely on dead reckoning or GPS. Celestial navigation uses angular measurements (sights) between the horizon and a celestial object.
The Sun is most often measured. Skilled navigators can use the Moon, planets or one of 57 "navigational stars" whose coordinates are tabulated. Celestial navigation is the process whereby angles between objects in the sky (celestial objects) and the horizon are used to locate one's position on the globe. At any given instant of time, any celestial object the Moon, Jupiter, or navigational star will be located directly over a particular geographic position on the Earth. This geographic position is known as the celestial object’s subpoint, and its location (its latitude and longitude) can be determined by referring to tables in a nautical almanac.
The measured angle between the celestial object and the horizon is directly related to the angle between the subpoint and the observer, and this measurement is used to define a circle on the surface of the Earth called a celestial line of position (LOP). The size and location of this circular line of position can be determined using mathematical or graphical methods. The LOP is significant because the celestial object would be observed to be at the same angle above the horizon from any point along its circumference at that instant.
