154 THE GREEK ASTRONOMY. 



same positions with respect to each other. This 

 stationary star is every night the same, and in the 

 same place ; the other stars also have the same 

 relative position ; but their general position at the 

 same time of night varies gradually from night to 

 night, so as to go through its cycle of appearances 

 once a year. All this would obviously agree with 

 the supposition that the sky is a concave sphere 

 or dome, that the stars have fixed places on this 

 sphere, and that it revolves perpetually and uni- 

 formly about the Pole or fixed point. 



But this supposition does not at all explain the 

 way in which the appearances of different nights 

 succeed each other. This, however, may be ex- 

 plained, it appears, by supposing the sun also to 

 move among the stars on the surface of the con- 

 cave sphere. The sun by his brightness makes the 

 stars invisible which are on his side of the heavens; 

 this we can easily believe; for the moon, when 

 bright, also puts out all but the largest stars ; and 

 we see the stars appearing in the evening, each 

 in its place, according to their degree of splendour, 

 as fast as the declining light of day allows them 

 to become visible. And as the sun brings day, and 

 his absence night, if he move through the circuit 

 of the stars in a year, we shall have, in the course 

 of that time, every part of the starry sphere in 

 succession presented to us as our nocturnal sky. 



This notion, that the sun moves round among 

 the stars in a year, is the basis of astronomy, 



