Astronomy for the use of schools and academies (1882) (14741203876)

Identifier: astronomyforuseo00gill (find matches)
Title: Astronomy for the use of schools and academies
Year: 1882 (1880s)
Authors: Gillet, J. A. (Joseph Anthony), 1837-1908 Rolfe, W. J. (William James), 1827-1910
Subjects: Astronomy
Publisher: New York : Potter, Ainsworth, & Co.
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress



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as at P and P it is said to be at its greatest elongation. ASTRONOMY. 31 126. Apparent Motion of an Inferior Pla7iet. — When theplanet is at P, if it could be seen at all, it would appearin the heavens at A. As it moves from P to P\ it willappear to move in the heavens from A to B. Then, as itmoves from Pr to P\ it will appear to move back againfrom B to A. While it moves from P to P\ it will appearto move from A to C; and, while moving from Pr to P,
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it will appear to move back again from C to A. Thus theplanet will appear to oscillate to and fro across the sun fromB to C, never getting farther from the sun than B on thewest, or C on the east: hence, when at these points, it issaid to be at its greatest western and eastern elongations.This oscillating motion of an inferior planet across the sun,combined with the suns motion anions: the stars, causes the 13- ASTRONOMY. planet to describe a path among the stars similar to thatshown in Fig. 145. 127. Phases of an Inferior Planet. — An inferior planet,when viewed with a telescope, is found to present a succes-sion of phases similar to those of the moon. The reasonof this is evident from Fig. 146. As an inferior planetpasses around the sun. it presents sometimes more andsometimes less of its bright hemisphere to the earth. Whenthe earth is at T. and Venus at superior conjunction, theplanet turns the whole of its bright hemisphere towards theearth, and appears full; it then becomes gi