PRECOMP NAVIGATION

Capt. P. V. H. Weems

Peer Reviewed

Abstract:	The Frontispiece shows the principle, equipment, and method for accomplishing celestial navigation. Fig. 1 shows how precomputed altitude curves are used for sea and air navigation, together with the navigator’s triangle, Napier’s Rules and Diagram, and selected formulae. Fig. 2 shows how altitude is precomputed for two dates, one for an aircraft sextant, and one for a marine sextant, together with the timed observations. These two pages are facing pages from the Navigator's Journal. Man’s ability to convert timed celestial observations to position on the Earth is the basis for navigation. Our first and greatest debt for this is to the astronomers and scientists who perfected the chronometer, sextant, almanac, telescope, and reduction tables about the middle of the eighteenth century. With 24hour availability of celestial observations, a Ailled navigator shoula know his position continuously within a mile. Celestial observations are timed sextant angles measured between the observed body and a reference, usually the sea horizon or artificial horizon substitute. When celestial observations are delayed, a (‘deduced reckoning” (DR) between fixes is required. To provide accurate DR over a period of several hours, billions have been spent on gyroscopic, inertial, and electronic equipment.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 16, Number 4
Pages:	424 - 427
Cite this article:	Weems, Capt. P. V. H., "PRECOMP NAVIGATION", NAVIGATION: Journal of The Institute of Navigation, Vol. 16, No. 4, Winter 1969-1970, pp. 424-427.
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