A Treatise on Astronomy, Theoretical and Practical Volume 1, PT. 2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1823 Excerpt: ...and D = 15' 33."8652, D 15' 33."8652.27293, P 57'4." 16844 I of continued fracti from the observed apparent semi-diameter of the Moon, we may 3 or, by the method of continued fractions, is nearly--. Hence, The ratio of the greatest and least apparent semi-diameters, is the same as the ratio of the perigean and apogean distances of the Moon, j the least apparent diameter 2.9' 30" _ 1--e the greatest apparent diameter 33' 30" 1-)-e' (if e be the eccentricity), whence e =.0635, whereas the eccentricity in the solar orbit only =, .0168. The equation of the centre then, in the lunar orbit, must be about 7 16'. If, therefore, we set off from a circular motion, and call that the regular one, the Moon's motion, besides the causes already assigned (see p. 639, ) will be still more irregular than the Sun's., always deduce the corresponding horizontal parallax by multiplying the former by and vice versa. The horizontal parallax of the Moon is the angle subtended by the Earth's radius at the Moon. Hence, the Earth not being spherical, the horizontal parallax is not the same, at the same instant of time, for all places on the Earth's surface. One proof that the Earth is not spherical, is by reversing this inference, namely, that the horizontal parallaxes computed for the same time are found not to be the same. Hence, in speaking of the horizontal parallax it is necessary to specify the place of observation. The Moon's parallax computed for Greenwich is different from the equatoreal parallax. Several corrections therefore, must be applied to an observed parallax, in order to compute, at the time of the observation, the Moon's distance from the centre of the Earth. For, that distance, it is plain, ought to result the same, whatever be the latitude o...