TIME AND SPACE DOUGI^AS 151 



AGE OF SUN 



One of the questions which has provoked controversy between 

 geologist, physicist, and astronomer for many years is the probable 

 age of the earth, an estimate of the age of the sun being, of course, 

 an upper limit to tlie age of the solar system. Jeans attacks the 

 problem from the new point of view, and his argument is as follows : 

 The sun is radiating away its mass at the rate of about 4,200,000 tons 

 per second and, if it were once as massive a star as Sirius now is, 

 then it has been radiating for 7X10^^ years. This means an age of 

 at least a million million years, and is several thousand times greater 

 than any previous estimate — a figure so great that it baffles compre- 

 hension, and staggers even the imagination. 



GALAXY EXPANDING 



There is an interesting consequence of loss of mass by radiation 

 which has an important bearing upon our system and upon the 

 galaxy of stars about us. If our sun be gradually diminishing in 

 mass, the law of conservation of momentum requires that the planets 

 move gradually off in ever expanding orbits. Similarly, if the mass 

 of our galaxy as a whole be gradually diminishing, the stars must 

 be opening out, spreading farther apart from the common center of 

 gravity and therefore from one another. Jeans estimates that 10^^ 

 years ago this galaxy was packed sixty-four times more closely than 

 it is at the present time. 



BINARY STARS 



This modifies various problems of cosmogony in a remarkable 

 manner. The orbits of binary stars have long been a mystery, because 

 no mutual force between two such stars was known which could 

 account for their being in such eccentric and large orbits about their 

 common center of gravity. Jeans points out that it is no longer 

 necessary to look for such a force, that with the enlarged time scale 

 , for the galaxy (greater than lO^'' years) outside influences become 

 not only possible but verj^ highly probable — that is to say, the normal 

 orbits of a binary system may be perturbed by the gravitational pull 

 of a passing star approaching more closely than is usual. The 

 chance of such an influence being brought to bear upon a binary is 

 greatly increased by the closer packing of the system in bygone ages. 

 Basing his calculations upon the observed percentage of decidedly 

 modified binary orbits and the probability of outside influence, 

 Jeans obtains an estimate of the age of the galaxy which confirms 

 his j)revious result of 10^^ years. 



