The navigator can extrapolate by means of navigational tables to acquire the position of each object for each minute of time. The Sun, Moon and Planets are perceived independently and are therefore specified separately however, only the star Aries is specified, while the other stars are assigned a set angular distance. The Almanac specifies for each whole hour of the year the position on the Earth's surface at which each body is directly overhead. ![]() These almanacs describe the positions and movements of celestial bodies, including the sun, moon, planets, and 57 stars chosen for their ease of identification and wide spacing. This geographic position is known as the celestial object's sub-point and its location, defined by latitude and longitude, can be determined from the tables of nautical or air almanacs. At any given instant of time, any celestial object such as the Earth's Moon, the planet Jupiter, or the navigational star Spica, one of the brightest stars in the nighttime sky, will be located directly over a particular geographic position on the Earth. Astronavigation calculates angles between objects in the sky (celestial objects) and the horizon to locate one's position on the globe. With the rise of the British Navy and merchant marine, the Greenwich Meridian or Prime Meridian at Greenwich, England eventually became the starting location for most celestial almanacs. In ancient times, the vessel's home port or home capital was used as the known location. ![]() Although the Sun is the most often measured celestial object, more sophisticated navigators are prepared to use our Moon, other planets, or one of 57 "navigational stars" described in nautical almanacs to observe the positions of these celestial objects relative to the observer and a known location. Astronavigation uses angular measurements or sightings between the horizon and a common celestial object to perform navigational problem-solving. ![]() , is a position-fixing process that has enabled sailors to cross featureless oceans with certainty and target unsighted land with precision.
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