THE 



POPULAR SCIENCE 



MONTHLY. 



NOVEMBER, 1900. 

 CHAPTERS ON THE STAES. 



By PROFESSOR SIMON NEWCOMB, U. S. N. 

 BINARY AND MULTIPLE SYSTEMS. 



SIE WILLIAM HEESCHEL was the first to notice that many stars 

 which, to the unaided vision, seemed single, were really composed 

 of two stars in close proximity to each other. The first question to 

 arise in such a case would he whether the proximity is real or whether 

 it is only apparent, arising from the two stars being in the same line 

 from our system. This question was speedily settled by more than 

 one consideration. If there were no real connection between any two 

 stars, the chances would be very much against their lying so nearly in 

 the same line from us as they are seen to do in the case of double stars. 

 ( hit of 5,000 stars scattered at random over the celestial vault the 

 chances would be against more than three or four being so close together 

 that the naked eye could not separate them, and would be hundreds to 

 one against any two being as close as the components of the closer 

 •double stars revealed by the telescope. The conclusion that the prox- 

 imity is in nearly all cases real is also proved by the two stars generally 

 moving together or revolving round each other. 



Altogether there is no doubt that in the case of the brighter stars 

 all that seem double in the telescope are really companions. But when 

 we come to the thousands or millions of telescopic stars, there may be 

 some cases in which the two stars of a pair have no real connection and 

 are really at very different distances from us. The stars of such a pair 

 are called 'optically double.' They have no especial interest for us 

 and need not be further considered in the present work. 



After Herschel, the first astronomer to search for double stars 

 ■on a large scale was Wilhelm Struve, the celebrated astronomer of 



