466 THbJ POPULAR SCIENCE MONTHLY. 



ft 



PLEASURES OF THE TELESCOPE. 



By GARRETT P. SP:RVISS. 

 III. THE STARRY HEAVENS [contirmed). 



THE zodiacal constellations of Gemini, Cancer, and Leo, to- 

 gether witli their neighbors Auriga, the Lynx, Hydra, Sex- 

 tans, and Coma Berenices, will furnish an abundance of occupa- 

 tion for our second night at the telescope. We shall begin, using 

 our three-inch glass, with a, the chief star of Gemini (map No. 4). 

 This is ordinarily known as Castor. Even an inexperienced eye 

 perceives at once that it is not as bright as its neighbor Pollux, )S. 

 Whether this fact is to be regarded as indicating that Castor was 

 brighter than Pollux in IGOo, when Bayer attached their Greek 

 letters is still an unsettled question. Castor may or may not be a 

 variable, but it is, at any rate, one of the most beautiful double 

 stars in the heavens. A power of one hundred is amply sufficient 

 to separate its components, whose magnitudes are about two and 

 three, the distance between them being 5'8", p, 230. A slight yet 

 distinct tinge of green, recalling that of the Orion nebula, gives a 

 peculiar appearance to this couple. Green is one of the rarest 

 colors among the stars. Castor belongs to the same general spec- 

 troscopic type in which Sirius is found, but its lines of hydrogen 

 are broader than those seen in the spectrum of the Dog Star. 

 There is reason for thinking that it may be surrounded with a 

 more extensive atmosphere of that gaseous metal called hydrogen 

 than any other bright star possesses. There seems to be no doubt 

 that the components of Castor are in revolution around their 

 common center of gravity, although the period is uncertain, vary- 

 ing in different estimates all the way from two hundred and fifty 

 to one thousand years ; the longer estimate is probably not far 

 from the truth. There is a tenth-magnitude star, distance 73", p. 

 164, which may belong to the same system. 



From Castor let us turn to Pollux, at the same time exchang- 

 ing our three-inch telescope for the four-inch, or, still better, the 

 five-inch. Pollux has five faint companions, of which we may 

 expect to see three, as follows : Tenth magnitude, distance 175", p. 

 70 ; nine and a half magnitude, distance 206", p. 90, and ninth 

 magnitude, distance 229", p. 75. Burnham has seen a star of thir- 

 teen and a half magnitude, distance 43", p. 275, and has divided 

 the tenth-magnitude star into two components, only 1'4" apart, 

 the smaller being of the thirteenth magnitude, and situated at the 

 angle 128. A calculation based on Dr. Elkin's parallax of 0'068" 

 for Pollux shows that that star may be a hundredfold more lumi- 

 nous than the sun, while its nearest companion may be a body 



