File:Astronomy for high schools and colleges (1881) (14761496014).jpg

Identifier: astronomyforhigh00newc (find matches)
Title: Astronomy for high schools and colleges
Year: 1881 (1880s)
Authors: Newcomb, Simon, 1835-1909 Holden, Edward Singleton, 1846-1914, joint author
Subjects: Astronomy
Publisher: New York, H. Holt and Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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thedusky ring so as to make it difficult to decide preciselywhere it ends and the dusky ring begins. The latter ex-tends about one half way from the inner edge of thebright ring to the ball of the planet. Aspect of the Rings.-—As Saturn revolves around thesun, the plane of the rings remains parallel to itself. Thatis, if we consider a straight line passing through the centreof the planet, perpendicular to the plane of the ring, asthe axis of the latter, this axis will always point in thesame direction. In this respect, the motion is similar to RING8 OF SATURK. 357 The ring of Saturn isorbit. Conse- that of the earth around the sun. inclined about 27° to the plane of its queutly, as the planet revolves around the sun, there is a change in the direction in which the sun shines upon it similar to that which produces the change of seasons upon the earth, as shown in Fig. 46, page 109. The corresponding changes for Saturn are siiown inFig. 97. During each revolution of Saturn the plane
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Fig. 97. -DIFFERENT ASPECTS OF THE RING OF SATURN AS SEENFROM THE EARTH. of the ring passes through the sun twice. This occurredin the years 1862 and 1878, at two opposite points of theorbit, as shown in the figure. At two other points, mid-way between these, the sun shines upon the plane of thering at its greatest inclination, about 27°. Since the earthis little more than one tenth as far from the sun as Sat-urn is, an observer always sees Saturn nearly, but notquite, as if he were upon the sun. Hence at certain times 358 ASTRONOMY. the rings of Saturn are seen edgeways, while at othertimes they are at an inclination of 27°, the aspect depend-ing upon the position of the planet in its orbit. The fol-lowing are the times of some of the phases : 1878, February 7th.—The edge of the ring was turnedtoward the sun. It could then be seen only as a thinline of light. 1885.—The planet having moved forward 90°, the southside of the rings may be seen at an inclination of 27°. 1891, Dece

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