PUTTING THE MOON IN THE POCKET ALMANAC

Robert W. Byerly

Peer Reviewed

Abstract: The omission of all moon data from the Pocket Almanac was recognized by the author of the Almanac as a ground for criticism. TWO reasons were given for omitting moon data. One of the reasons was that "the moon is little used." It is no doubt true that the moon is not much used in routine navigation, but in some situations the moon is of critical importance to the navigator. In the daytime, the moon enables the navigator to obtain a point fix. When dead reckoning is uncertain because of an unknown current or wind, two or even more position lines obtained from observations of the sun taken several hours apart may have apparent crossing points several miles from the true positi0n.l In this situation, the only astronomical means which can give the navigator his true position is a moon sight taken at the time of a sun sight. In the night, the moon may provide a line of position which can be obtained in no other way. When the altitude of the moon is not too high, the moon sometimes lights the horizon below it sufficiently to permit the taking of a sight. It thus provides a means, and the only celestial means, by which a marine navigator may be able to obtain accurate data as to his position during the sometimes long interval between evening twilight and morning twilight. Moon data thus has a very practical value for the navigator.
Published in: NAVIGATION, Journal of the Institute of Navigation, Volume 4, Number 6
Pages: 250 - 258
Cite this article: Byerly, Robert W., "PUTTING THE MOON IN THE POCKET ALMANAC", NAVIGATION, Journal of The Institute of Navigation, Vol. 4, No. 6, 1955, pp. 250-258.
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