Astronomy for the use of schools and academies (1882) (14764141215)

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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ious other indications, we conclude that theearth is a spliere. 56. Size of the Earth.—The size of the earth is ascer-tained by measuring the length of a degree of a meridian,and multiplying this by three hundred and sixty. This givesthe circumference of the earth as about twenty-five thousandmiles, and its diameter as about eight thousand miles. Weknow that the two stations between which we measure areone degree apart when the elevation of the pole at onestation is one degree greater than at the other. 57. The Earth Flattened at the Poles. — Degrees on themeridian have been measured in various parts of the earth,and it has been found that they invariably increase in length ASTRONOMY. 56 as we proceed from the equator towards the pole : hencethe earth must curve less and less rapidly as we approach thepoles; for the less the curvature of a circle, the larger the degrees on it. 58 The Earth in Space. —In Fig. 68 we have a viewof the earth suspended in space. The side of the earth
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Fig. 68. turned towards the sun is illumined, and the other side is indarkness. As the planet rotates on its axis, successive por-tions of it will be turned towards the sun. As viewed froma point in space between it and the sun. it will presentlight and dark portions, which will assume different formsaccording to the portion which is illumined. These differ-ent appearances are shown in Fig. 69. ASTRONOMY, 57 Day axd Night.59. Day and Night. — The succession of day and night