CHAPTER XLI. 

 THE STARS (continued). 



DOUBLE AND MULTIPLE STARS- COLOURED AND VARIABLE STARS 



CLUSTERS, GROUPS, AND NEBUL/E THE GALAXY, OR MILKY WAY 



HOW TO FIND OUT THE PRINCIPAL STARS. 



ALTHOUGH not very clearly visible to the naked eye, there are in the sky 

 some pairs of stars very close together apparently ; but when these double 

 stars are examined with a good telescope we find that 

 though we fancy they are two stars very close, in reality 

 an immense distance separates them. By Vega, which 

 we have already mentioned, there is apparently a star, 

 which on examination will be found really to be two 

 stars. It is also in the constellations of the Lyre, but of 

 much lower magnitude than Vega. But in some instances 

 there are three or four stars thus placed together, and 



Fig. 6x2. ? Leonis. r 



the frequency of the occurrence of this fact establishes 

 the farther fact that these combinations are not accidental that the stars 

 are interdependent and physically connected. 



There are now at least six thousand double stars known,* and this is a 

 very small proportion of the forty millions or so of suns which are believed to 

 exist in space. But of these six thousand a larger proportion have been 

 ascertained to be physically connected. More than six hundred of these pairs 

 are double suns, while again there are other combinations of three and per- 

 haps more. When two are thus connected we have what are termed binary 

 systems, and when more are associated they are called triple and multiple 

 stars. An example of the last-mentioned class is the small star above 

 mentioned near Vega. It is e Lyrae, and is a double of a double. In 

 ordinary telescopes this will not be perceived, but with a high power the 

 combination will be noticed. The same phenomenon is observable in one 

 of the stars of Hercules and in Andromeda. 



The revolution of these double suns, or binary systems, has been closely 

 observed, and Professor Newcomb has given us a list of the binary systems 

 of short period which are well determined. These are as follows : 



* Mr. Burnham has lately given a list of two hundred and fifty-one new double stars, 

 and in the Astronomical Society's proceedings there is a list of ten thousand. 



