Astronomy for the use of schools and academies (1882) (14577488550)

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

Text Appearing Before Image:

Fig. 123. greatly exaggerated in the upper portion of the diagram. Theform of her path is given with a greater degree of accuracy inthe lower part of the figure (the broken line represents the path ASTRONOMY. I07 of the earth): but even here there is considerable exaggeration.The complete serpentine path of the moon around the sun isshown, greatly exaggerated, in Fig. 123, the broken line beingthe path of the earth. The path described by the moon through space is much thesame as that described by a point on the circumference of awheel which is rolled over another wheel. If we place a cir-cular disk against the wall, and carefully roll along its edgeanother circular disk (to which a piece of lead pencil has been

Text Appearing After Image:

Fig. 124. fastened so as to mark upon the wall), the curve described willsomewhat resemble that described by the moon. This curveis called an epicycloid, and it will be seen that at every pointit is concave towards the centre of the larger disk. In thesame way the moons orbit is at eveiy point concave towardsthe sun. The exaggeration of the sinuosity in Fig. 123 will be moreevident when it is stated, that, on the scale of Fig. 124, the io8 ASTRONOMY. whole of the serpentine curve would lie within the breadth ofthe fine circular line MM, 109. The Lunar Day.— The lunar day is twenty-ninetimes and a half as long as the terrestrial day. Near themoons equator the sun shines without intermission nearlyfifteen of our days, and is absent for the same length oftime. Consequently, the vicissitudes of temperature towhich the surface is exposed must be very great. Duringthe long lunar night the temperature of a body on themoons surface would probably fall lower than is ever knownon the earth, w

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1882

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