$ 40 Hipparchus 51 



the other is known. Hipparchus knew that the sun was 

 very much more distant than the moon, and appears to 

 have tried more than one distance, that of Aristarchus among 

 them, and the result obtained in each case shewed that 

 the distance of the moon was nearly 59 times the radius 

 of the earth. Combining the estimates of Hipparchus and 

 Aristarchus, we find the distance of the sun to be about 1,200 

 times the radius of the earth a number which remained sub- 

 stantially unchanged for many centuries (chapter vin., 161 ). 



42^The appearance in 134 B.C. of a new star in the 

 Scorpion is said to have suggested to Hipparchus the 

 construction of a new catalogue of the stars. * He included 

 i, 080 stars, and not only gave the (celestial) latitude and 

 longitude of each star, but divided them according to their 

 brightness into six magnitudes. The constellations to which 

 he refers are nearly identical with those of Eudoxus ( 26), 

 and the list has undergone few alterations up to the present 

 day, except for the addition of a number of southern con- 

 stellations, invisible in the civilised countries of the ancient 

 world. Hipparchus recorded also a number of cases in 

 which three or more stars appeared to be in line with one 

 another, or, more exactly, lay on the same great circle, 

 his object being to enable subsequent observers to detect 

 more easily possible changes in the positions of the stars. 

 The catalogue remained, with slight alterations, the standard 

 one for nearly sixteen centuries (cf. chapter in., 63). 



The construction of this catalogue led to a notable 

 discovery, the best known probably of all those which 

 Hipparchus made. In comparing his observations of certain 

 stars with those of Timocharis and Aristyllus ( 33), made 

 about a century and a half earlier, Hipparchus found that 

 their distances from the equinoctial points had changed. 

 Thus, in the case of the bright star Spica, the distance 

 from the equinoctial points (measured eastwards) had 

 increased by about 2 in 150 years, or at the rate of 48'' per 

 annum. Further inquiry showed that, though the roughness 

 of the observations produced considerable variations in the 

 case of different stars, there was evidence of a general 

 increase in the longitude of the stars (measured from west 

 to east), unaccompanied by any change of latitude, the 

 amount of the change being estimated by Hipparchus as 



