I2O 



A Short History of Astronomy 



[CH. IV. 



from the sun), the motion of the earth itself being directly 

 to or from Jupiter produces no effect on the apparent 

 motion of Jupiter (since any displacement directly to or 

 from the observer makes no difference in the object's 

 place on the celestial sphere) ; but Jupiter itself is actually 

 moving towards the left, and therefore the motion of 



FIG. 48. The stationary points of Jupiter. 



Jupiter appears to be also from right to left, or from west 

 to east. Hence, as before, between j, and j and between 

 j and J 2 there must be points / j\ (Jan. 24 and May 27, 

 in fig. 6) at which Jupiter appears for the moment to be 

 stationary. 



The actual discussion of the stationary points given by 

 Coppernicus is a good deal more elaborate and more 

 technical than the outline given here, as he not only shews 



