GALILEO AND HIS JUDGES. 65 



such argument, because the appearances in question 

 result from the different relative positions of the Earth 

 and Sun at different seasons of the year, and would 

 be the same whichever of the two bodies were in 

 motion. 



There follows some conversation arising from one of 

 the anti-Copernican books of that day ; one of the 

 difficulties suggested, being the vast distance at which 

 you must suppose the fixed stars to be placed, if 

 Copernicus be right. We who are accustomed to the 

 idea of these immense distances, can scarcely under- 

 stand the prejudices of the philosophers of that age 

 against admitting them. And it is worth noting that 

 Galileo takes for granted, while answering these 

 theoretical objections, the calculation of his prede- 

 cessors that the distance of the Sun is that of 1,208 

 semi-diameters of the Earth, that is something more 

 than 4,800,000 miles, about one-nineteenth part of 

 what we now know it to be. So also he supposes the 

 size of the Sun to be much less than what is really 

 the case. He was also under the erroneous impression, 

 arising doubtless from the imperfection of the instru- 

 ments he used, that the stars really had an apparent 

 diameter, though less than Tycho Brahe and other 

 astronomers had supposed, and estimates the angular 

 diameter of a star of the first magnitude at about 

 5" ; consequently he imagined the stars to be 

 much nearer than is actually the fact. It is well 

 known to modern observers, that the apparent size of 

 a star is the effect of an optical illusion, and that 



