The Romance of the Heavens 13 



a very small patch of that pale-white belt, the Milky Way, 

 which spans the sky at night. It is true that this is a par- 

 ticularly rich area of the Milky Way, but the entire belt of light 

 has been resolved in this way into masses or clouds of stars. 

 Astronomers have counted the stars in typical districts here and 

 there, and from these partial counts we get some idea of the 

 total number of stars. There are estimated to be between two 

 and three thousand million stars. 



Yet these worlds are separated by inconceivable distances 

 from each other, and it is one of the greatest triumphs of modern 

 astronomy to have mastered, so far, the scale of the universe. For 

 several centuries astronomers have known the relative distances 

 from each other of the sun and the planets. If they could discover 

 the actual distance of any one planet from any other, they could 

 at once tell all the distances within the Solar System. 



The sun is, on the latest measurements, at an average dis- 

 tance of 92,830,000 miles from the earth, for as the orbit of the 

 earth is not a true circle, this distance varies. This means that 

 in six months from now the earth will be right at the opposite 

 side of its path round the sun, or 185,000,000 miles away from 

 where it is now. Viewed or photographed from two positions so 

 wide apart, the nearest stars show a tiny "shift" against the 

 background of the most distant stars, and that is enough for the 

 mathematician. He can calculate the distance of any star near 

 enough to show this "shift." We have found that the nearest 

 star to the earth, a recently discovered star, is twenty-five trillion 

 miles away. Only thirty stars are known to be within a hundred 

 trillion miles of us. 



This way of measuring does not, however, take us very far 

 away in the heavens. There are only a few hundred stars within 

 five hundred trillion miles of the earth, and at that distance the 

 "shift" of a star against the background (parallax, the astrono- 

 mer calls it) is so minute that figures are very uncertain. At this 

 point the astronomer takes up a new method. He learns the 



