Astronomy for the use of schools and academies (1882) (14577775089)

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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cal Nebula. — While manynebulae are circular in form, others are elliptical. The for-mer are called circular nebulae, and the latter ellipticalnebulae. Elliptical nebulae have been discovered of everydegree of eccentricity. Examples of various circular andelliptical nebulae are given in Fig. 430. 1 B Fig. 429. 372. Annular Nebula. — Occasionally ring-shaped nebu-lae have been observed, sometimes with, and sometimeswithout, nebulous matter within the ring. They are calledannular nebulae. They are both circular and elliptical inform. Several specimens of this class of nebulae are givenin Fig. 431. 373. Nebulous Stais. — Sometimes one or more minutestars are enveloped in a nebulous haze, and are hencecalled nebulous stars. Several of these nebulae are shownin Fig. 432. 374. Spiral Nebula. — Very many nebulae disclose amore or less spiral structure, and are known as spiralnebulae. They are illustrated in Fig. 433. There are, how- 374 ASTRONOMY. : 1 0 3G 9 /■■ 4 5 7 8 Fig. 430.
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ASTRONOMY. 375 ever, a great variety of spiral forms. We shall have occa-sion to speak of these nebulae again (381-383). 375. Double and Multiple NebuIce. — Many double and 1 2 4 5 5 6 Fig. 432. multiple nebulae have been observed, some of which arerepresented in Fig. 434. Fig. 435 shows what appears to be a double annularnebula. Fig. 436 gives two views of a double nebula. #®F 1& f 1 Fig. 433- The change of position in the components of this doublenebula indicates a motion of revolution similar to that ofthe components of double stars. 376 ASTRONOMY. Irregular Nebulae. 376. Irregular Forms. — Besides the more or less regu-lar forms of nebulae which have been classified as indicated 1 2 * * 4 3 Fig. 437 shows Fig. 434- above, there are many of very irregular shapes, and someof these are the most remarkable nebulae in the heavens.a curiously shaped nebula, seen by SirJohn Herschel in the southernheavens; and Fig. 438, one inTaurus\ known as the Crabnebula. 377. The Great Nebul