COPERNICAN SYSTEM. 



33 



Venus, Copernicus supposed them to be revolving around the sun, 

 but in orbits within the earth's. This would explain why they 

 were never seen at any considerable distance from that luminary 

 and also the various irregularities observed in their motions, 

 Thus : 



Let S be the sun, E the earth, and V, Venus. In the situation 

 represented in the diagram Venus would appear among the stars 

 at A, the sun being at B. In this case, supposing the earth to 

 turn on its axis in the direction of the arrow, the sun would come 

 to the meridian or overhead, to an observer on its'surface, before 

 the planet, which consequently, setting after the sun, would be the 

 evening star. Now supposing the earth stationary in its orbit, let 

 Venus move from V to W. This would cause her to describe 

 the arc A C in the heavens, gradually approaching the sun, which 

 is apparently at B, and then appearing 011 the opposite side. 

 When in the position W, still supposing the earth to turn on its 

 axis in the direction of the arrow, Venus would come to the 

 meridian, or rise before the sun and consequently be morning 

 star During the rest of her revolution in her orbit, from W to V 

 she would seem to move backwards in the heavens, or retrograde 

 from C to A, and at the points C and A she would appear for a 

 short time stationary. We have supposed the earth to be at rest, 



