File:Astronomy for the use of schools and academies (1882) (14763997992).jpg

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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pposite points ofSaturns orbit in which the rings are turned edgewise tcus, and two points half-way between the former in whicrthe ring is seen at its maximum inclination of about twenty-seven degrees. Since the planet performs a revolution irtwenty-nine years and a half, these phases occur at averageintervals of about seven years and four months. ASTRONOMY. 267 272. Disappearance of Saturns Ring.— It will be seenfrom Fig. 297 that the plane of the ring may not be turnedtowards the sun and the earth at exactly the same time, andalso that the earth may sometimes come on one side of theplane of the ring while the sun is shining on the other. Inthe figure, E, E, E\ and E is the orbit of the earth.When Saturn is at S, or opposite, at E, the plane of the ringwill pass through the sun, and then only the edge of the ringwill be illumined. Were Saturn at S, and the earth at E, theplane of the ring would pass through the earth. This wouldalso be the case were the earth at E, and Saturn at S.
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Fig. 298. Were Saturn at S or at S/f, and the earth farther to the left orto the right, the sun would be shining on one side of the ringwhile we should be looking on the other. In all these casesthe ring will disappear entirely in a telescope of ordinarypower. With very powerful telescopes the ring will appear, inthe first two cases, as a thin line of light (Fig. 298). It willbe seen that all these cases of disappearance must take placewhen Saturn is in the parts of his orbit intercepted betweenthe parallel lines A C and BD. These lines are tangent tothe earths orbit, which they enclose, and are parallel to theplane of Saturns ring. As Saturn passes away from thesetwo lines on either side, the rings appear more and more open.When the dark side of the ring is in view, it appears as a 268 ASTRONOMY. black line crossing the planet; and on such occasions the sun-light reflected from the outer and inner edges of the rings Aand B enables us to see traces of the ring on each side ofSaturn, a

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