Astronomy for the use of schools and academies (1882) (14741266356)

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

Text Appearing Before Image:

Fig. 22Q. For the present it remains, like a few other lines in the spec-trum, an unexplained mystery. Besides bright lines, the corona shows also a faint continu-ous spectrum, in which have been observed a few of the moreprominent dark lines of the solar spectrum. This shows, that, while the corona may be in the maincomposed of glowing gas (as indicated by the bright linesof its spectrum), it also contains considerable matter in such 2IO ASTRONOMY. a state as to reflect the sunlight, probably in the form of dustor fog. V. ECLIPSES. 205. The Shadows of the Earth and Moon. — Theshadows cast by the earth and moon are shown in Fig. 235.

Text Appearing After Image:

Fig. 230. Each shadow is seen to be made up of a dark portioncalled the umbra, and of a lighter portion called thepenitmbra. The light of the sun is completely excludedfrom the umbra, but only partially from the penumbra.The umbra is in the form of a cone, with its apex awayfrom the sun; though in the case of the earths shadowit tapers very slowly. The penumbra surrounds the umbra, ASTRONOMY. 21 I and increases in size as we recede from the sun. The axisof the earths shadow lies in the plane of the ecliptic, whichin the figure is the surface of the page. As the moonsorbit is inclined five degrees to the plane of the ecliptic,the axis of the moons shadow will sometimes lie above,

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1882

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