File:Astronomy for high schools and colleges (1881) (14740851406).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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telescope employedhas an important effect on the appearances seen, have kept thismethod from a wide utility, which it at first seemed to promise. The apparent diameters of these satellites have been measured byStkuve, Secchi, and others, and the best results are : I, 10; II, 0-9; III, l-5; IV, l-3. Their masses (Jupiter =^1) are : I, 0-000017; II, 0000023; III, 0000088; IV, 0*000043. The third satellite is thus the largest, and it has about the den-sity of the planet. The true diameters vary from 2200 to 3700miles. The volume of II is about that of our moon ; III approachesour earth in size. Variations in the light of these bodies have constantly beennoticed which have been supposed to be due to the fact that theyturned on their axes once in a revolution, and thus presented variousfaces to us. The recent accurate photometric measures of Engel-MANN show that this hypothesis will not account for all the changesobserved, some of which appear to be quite sudden. SATELLITES OF JUPITER. 351
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CHAPTER VIII. SATURN AND ITS SYSTEM.§ 1. GENERAL DESCRIPTION. Saturn is tlie most distant of the major planets knownto the ancients. It revolves around the sun in 29J years,at a mean distance of nearly 1,500,000,000 kilometres(890,000,000 miles). The angular diameter of the ball ofthe planet is about 16^ • 2, corresponding to a true diam-eter of about 110,000 kilometres (70,500 miles). Its diam-eter is therefore nearly nine times and its volume about700 times that of the earth. It is remarkable for its smalldensity, which, so far as known, is less than that of anyother heavenly body, and even less than that of water.Consequently, it cannot be composed of rocks, like thosewhich form our earth. It revolves on its axis, accordingto the recent observations of Professor Hall, in 10* 1424% or less than half a day. Saturn is perhaps the most remarkable planet in the so-lar system, being itself the centre of a system of its own,altogether unlike any thing else in the heavens. Its mostnotew

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