. A treatise on surveying and navigation: uniting the theoretical, the practical, and the educational features of these subjects. nter,and this reduction is called working a lunar, which is generally thehighest scientific ambition of the young navigator. \ The true distance between the sun and moon, or between a starand the moon, can be deduced from the apparent distance by theapplication of spherical trigonometry. The moon is never seen by an observer in its true place, unless theobserver is in a line between the center of the earth and the moon,that is, unless the moon is in the zenith of th
. A treatise on surveying and navigation: uniting the theoretical, the practical, and the educational features of these subjects. nter,and this reduction is called working a lunar, which is generally thehighest scientific ambition of the young navigator. \ The true distance between the sun and moon, or between a starand the moon, can be deduced from the apparent distance by theapplication of spherical trigonometry. The moon is never seen by an observer in its true place, unless theobserver is in a line between the center of the earth and the moon,that is, unless the moon is in the zenith of the observer; in all other * There are nine lunar stars, Arietis, Aldebaran, Pollax, Regulus, Spica,Antares, Aquilae, Fomalhaut, and Pegasi. + Many navigators, both old and young, direct all their efforts to knowing howto do, without attempting to comprehend the reasons for so doing ; and this theworld calls practical, — a complete perversion of the term. On the otherhand, some men of the schools spend their energies in metaphysical nothings,splitting hairs in logic, and calling it scientific ; this is equally a 222 NAVIGATION. positions, the moon is depressed by parallax, and appears nearer tothose stars that are below her, and further from those stars that areabove her, than would appear from the center of the earth. There-fore, the apparent altitudes of the two objects, must be taken at thesame time that their distance asunder is measured. The altitudesmust be corrected for parallax and refraction, thus obtaining thetrue altitudes. The annexed figure is a general representationof the triangles pertaining to a lunar observation. Let Z be the zenith of an observer, S theapparent place of the sun or star, and *S its trueplace. Also, let m be the apparent place of themoon, and m its true place as seen from the cen-ter of the earth. Here are two distinct triangles, ZSm, and ZSm. The apparentaltitudes subtracted from 90°, give ZS and Zm, and Sm is theapparent distanc
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Keywords: ., boo, bookcentury1800, booksubjectnavigation, booksubjectsurveying
