Line of Position

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A Line Of Position or position line may be derived from celestial observations or observation of terrestrial objects whose location is known.

The combination of the angle of observation of a celestial body (sun, moon, planet, star) with an exact time of day allows the observer to calculate one line of position on the face of the earth that corresponds to that observation.

Observations of two celestial bodies (or two terrestrial objects) and two lines of position allow a navigator to "fix" a position, in theory. Limits of the instruments, movement between two observations, the precision of the chronometer, and the skill of the observer affect the precision of a calculated position.

Once a line of position has been determined, an advanced line of position may be drawn on the map to aid dead reckoning from the known line to a line that passes through one's destination. The task for the navigator is then to determine when the advanced LOP is reached; if the destination is not reached at that point, the navigator must decide to turn one way or the other on the advanced LOP to reach the destination.

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