ALEXANDRIAN OR HELLENISTIC PERIOD 



deed, it is more than likely that he did so the elements 

 of error in his measurements would still have kept 

 him wide of the true figures. 



The chief studies of Hipparchus were directed, as 

 we have seen, towards the sun and the moon, but a 

 phenomenon that occurred in the year 134 B.C. led 

 him for a time to give more particular attention to the 

 fixed stars. The phenomenon in question was the 

 sudden outburst of a new star; a phenomenon which 

 has been repeated now and again, but which is suffi- 

 ciently rare and sufficiently mysterious to have ex- 

 cited the unusual attention of astronomers in all gen- 

 erations. Modern science offers an explanation of the 

 phenomenon, as we shall see in due course. We do 

 not know that Hipparchus attempted to explain it, 

 but he was led to make a chart of the heavens, probably 

 with the idea of guiding future observers in the ob- 

 servation of new stars. Here again Hipparchus was 

 not altogether an innovator, since a chart showing the 

 brightest stars had been made by Eratosthenes; but 

 the new charts were much elaborated. 



The studies of Hipparchus led him to observe the 

 stars chiefly with reference to the meridian rather than 

 with reference to their rising, as had hitherto been the 

 custom. In making these studies of the relative po- 

 sition of the stars, Hipparchus was led to compare his 

 observations with those of the Babylonians, which, it 

 was said, Alexander had caused to be transmitted to 

 Greece. He made use also of the observations of 

 Aristarchus and others of his Greek precursors. The 

 result of his comparisons proved that the sphere of 

 the fixed stars had apparently shifted its position in 



VOL. I. 16 241 



