. Astronomy for high schools and colleges . f large quantities of hydrogen inthe envelope. Sodium and magnesium lines are also seen, andothers yet fainter. Type II is composed mainly of the yellow stars, like our ownsun, Arcturus, Capella, Aldelaran, and Pollux. The spectrum ofthe sun is shown in the second place in the plate. The vast ma-jority of the stars visible to the naked eye belong to this class. Type III (see the third and fourth spectra in the plate) is com-posed of the brighter reddish stars like a Orionis, Antares, a Herculis,etc. These spectra are much contracted toward the violet
. Astronomy for high schools and colleges . f large quantities of hydrogen inthe envelope. Sodium and magnesium lines are also seen, andothers yet fainter. Type II is composed mainly of the yellow stars, like our ownsun, Arcturus, Capella, Aldelaran, and Pollux. The spectrum ofthe sun is shown in the second place in the plate. The vast ma-jority of the stars visible to the naked eye belong to this class. Type III (see the third and fourth spectra in the plate) is com-posed of the brighter reddish stars like a Orionis, Antares, a Herculis,etc. These spectra are much contracted toward the violet end, andare crossed by eight or more dark bands, thes^ bands being them-selves resolvable into separate lines. These three types comprise nearly all the lucid stars, and it isnot a little remarkable that the essential differences between thethree classes were recognized by Sir Willtam Herschel as earlyas 1798, and published in 1814. Of course his observations weremade without a slit to his spectroscopic apparatus. HPEiJTllA. 469. 470 ASTRONOMY. Type IV comprises the red stars, which are mostly characteristic spectrum is shown in the last figure of the is curiously banded with three bright spaces separated bydarker ones. It is probable that the hotter a star is the more simple a spectrumit has ; for the brightest, and therefore probably the hottest stars,such as Sirius, give spectra showing only very thick hydrogen linesand a few very thin metallic lines, while the cooler stars, such asour sun, are shown by their spectra to contain a much larger num-ber of metallic elements than stars of the type of Sirius, but nonon-metallic elements (oxygen possibly excepted). The cooleststars give band-spectra characteristic of compounds of metallicwith non-metallic elements, and of the non-metallic elements un-combined. § 2. MOTION OP STABS IN THE LINE OP SIGHT. Spectroscopic observations of stars not only give information inregard to their chemical and ph
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