File:Astronomy for high schools and colleges (1881) (14740845966).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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mountain-chains have been detected. Thelowest surface of the moon which can be seen with thetelescope appears to be nearly smooth and flat, or, tospeak more exactly, spherical (because the moon is asphere). This surface has different shades of color indifferent regions. Some portions are of a bright, silverytint, while others have a dark gray appearance. These dif-ferences of tint seem to arise from differences of material. Upon this surface as a foundation are built numerousformations of various sizes, but all of a very simple char-acter. Their general form can be made out by the aid ofFig. 89, and their dimensions by the scale of miles atthe bottom of it. The largest and most prominentfeatures are known as craters. They have a typical formconsisting of a round or oval rugged wall rising from theplane in the manner of a circular fortiflcation. These THE MOONS SURFACE. 329 walls are frequently from three to six thousand metres inheight, yQvy rough and broken. In their interior we see
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ASPECT OF THE MOONS SURFACE. the plane surface of the moon abeady described. It is,however, generally covered with fragments or broken up 330 ASTHOHOMir. by small inequalities so as not to be easily made out. Inthe centre of the craters we frequently find a conical for-mation rising up to a considerable height, and much largerthan the inequalities just described. In the craters wehave a vague resemblance to volcanic formations upon theearth, the principal difference being that their magnitudeis very much greater than any thing known here. Thediameter of the larger ones ranges from 50 to 200 kilo-metres, while the smallest are so minute as to be hardlyvisible with the telescope. When the moon is only a few days old, the suns raysstrike very obliquely upon the lunar mountains, and theycast long shadows. From the known position of the sun,moon, and earth, and from the measured length of theseshadows, the heights of the mountains can be calculated.It is thus found that some of the mountai

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