File:Astronomy for high schools and colleges (1881) (14783747383).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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omeda) gives a continuous spectrum, while the nebulaof Orion^ which fairly glistens with small stars, has a discontinuous Jr :Ba IT M^ — Fig. 131.—spectrum of a tlaketary nebula. spectrum, showing it to be a true gas. Most of these stars are toofaint to be separately examined with the spectroscope, so that wecannot say whether they have the same spectrum as the nebulae. The spectrum of most clusters is continuous, indicating that theindividual stars are truly stellar in their nature. In a few cases,however, clusters are composed of a mixture of nebulosity (usuallynear their centre) and of stars, and the spectrum in such cases iscompound in its nature, so as to indicate radiation both by gaseousand solid matter. § 5. DISTRIBUTION OF NEBULA AND CLUSTERSON THE SURFACE OF THE CELES-TIAL SPHERE. The following map (Fig. 132) by Mr. R. A. Proctor, gives at aglance the distribution of the nebulae on the celestial sphere withreference to the Milky Way, whose boundaries only are indicated.
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STAR-CLUSTERS. 467 The position of each nebula is marked by a dot; where the dots arethickest there is a region rich in nebulae. A casual examinationshows that such rich regions are distant from the Galaxy, and itwould appear that it is a general law that the nebulae are distri-buted in greatest number around the two poles of the galacticcircle, and that in a general way their number at any point of thesphere increases with their distance from this circle. This wasnoticed by the elder Herschel, who constructed a map similar tothe one given. It is precisely the reverse of the law of apparentdistribution of the true star-clusters, which in general lie in or nearthe Milky Way. CHAPTER V. SPECTRA OF FIXED STARS. 1. CHARACTERS OF STELLAR SPECTRA. Soon after the discovery of the spectroscope, Dr. Huggins andProfessor W. A. Miller applied this instrument to the examina-tion of stellar spectra, which were found to be, in the main, similarto the solar spectrum—i.e., composed of a continuous

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