Astronomy for amateurs (1904) (14781502214)

Identifier: astronomyforamat00flam (find matches)

Title: Astronomy for amateurs

Year: 1904 (1900s)

Authors: Flammarion, Camille, 1842-1925 Welby, Frances A. (Frances Alice) tr

Subjects: Astronomy

Publisher: New York, D. Appleton and company

Contributing Library: The Library of Congress

Digitizing Sponsor: The Library of Congress

Text Appearing Before Image:

ce,4h. 18 30, insteadof 4h. i8m. 30s. This makes clear the distinction between the relativemeasure of an angle and the absolute measures, such,for instance, as the meter. Thus, a degree may bemeasured on this page, while a second (the 3,600th partof a degree) measured in the sky may correspond tomillions of kilometers. Now the measure of the Moons diameter gives usan angle of a little more than half a degree. If it wereexactly half a degree, we should know by that that itwas 114 times the breadth of its disk away from us.But it is a little less, since we have more than half adegree (3i0j ^^i^ the geometric ratio tells us that thedistance of our satellite is no times its diameter. Hence we have very simply obtained a first idea ofthe distance of the Moon by the measure of its diameter. 290 ON METHODS Nothing could be simpler than this method. The firststep is made. Let us continue. This approximation tells us nothing as yet of thereal distance of the orb of night. In order to know this

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Fig. 8i.—Division of the Circumference into 360 degrees. distance in miles, we need to know the width in miles of the lunar disk. This problem has been solved, as follows: Two observers go as far as possible from each other, and observe the Moon simultaneously, from two stations situated on the same meridian, but having a wide differ- 20 291 ASTRONOMY FOR AMATEURS ence of latitude. The distance that separates the twopoints of observation forms the base of a triangle, ofwhich the two long sides come together on the Moon. It is by this proceeding that the distance of oursatellite was finally established, in 1751 and 1752, bytwo French astronomers, Lalande and Lacaille; theformer observing at Berlin, the latter at the Cape ofGood Hope. The result of their combined observations

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