Cambridge Encyclopedia » Cambridge Encyclopedia Vol. 53

navigation - Modern methods, Celestial navigation, History, Austronesian Navigation, "Point system" measure of direction, Sources

position time craft line

The means of finding the way from one place to another in safety. Celestial navigation is the oldest and most traditional type of navigation. Navigators could calculate their craft's latitude from the angle of the sun or other stars above the horizon, measured using a sextant. Longitude was calculated by knowing the local time exactly compared to that at 0° longitude, at Greenwich, London. Time is based on the time of rotation of the Earth, and is measured aboard ship using a very accurate chronometer. The simplest form of navigation is called dead reckoning (from the term deduced reckoning): the position of a ship or aircraft is simply calculated by knowing its speed (measured in knots), the direction it is heading from a compass reading (the bearing), and the time it has been travelling. Navigators can improve on the dead reckoning position if they take account of effects of wind and tide pushing their craft off course. The result is a plot of their estimated position. Another type of navigation, known as piloting, uses features along the route as landmarks (eg tall buildings, hills, towers). Navigators use a compass to measure the bearing of a landmark. If they then draw a line on the map from the landmark, at that bearing, they create a position line. Their craft is somewhere on that line. If they locate other landmarks and repeat the process, they will determine a point where the lines cross. This is a fix and it determines the position of the craft.

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over 7 years ago

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over 7 years ago

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almost 8 years ago

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