158 THE GREEK ASTRONOMY. 



1. Fixity of the Stars, The question necessarily arose after the dis- 

 covery of the precession, even if such a question had never suggested 

 itself before, whether the stars which were called fixed, and to which 

 the motions of the other luminaries are referred, do really retain con- 

 stantly the same relative position. In order to determine this funda- 

 mental question, Hipparchus undertook to construct a Map of the 

 heavens ; for though the result of his survey was expressed in words, 

 we may give this name to his Catalogue of the positions of the most 

 conspicuous stars. These positions are described by means of alinea- 

 tions that is, three or more such stars are selected as can be touched 

 by an apparent straight line drawn in the heavens. Thus Hipparchus 

 observed that the southern claw of Cancer, the bright star in the same 

 constellation which precedes the head of the Hydra, and the bright 

 star Procyon, were nearly in the same line. Ptolemy quotes this and 

 many other of the configurations which Hipparchus had noted, in 

 order to show that the positions of the stars had not changed in the 

 intermediate time ; a truth which the catalogue of Hipparchus thus 

 gave astronomers the means of ascertaining. It contained 1080 stars. 



The construction of this catalogue of the stars by Hipparchus is an 

 event of great celebrity in the history of astronomy. Pliny, 1 who 

 speaks of it with admiration as a wonderful and superhuman task 

 (" ausus rem etiam Deo improbam, annumerare posteris stellas"), as- 

 serts the undertaking to have been suggested by a remarkable astro- 

 nomical event, the appearance of a new star ; " novam stellam et aliam 

 in sevo suo genitam deprehendit ; ej usque motu, qua die fulsit, ad 

 dubitationem est adductus anne hoc saepius fieret, moverenturque et 

 eae quas putamus affixas." There is nothing inherently improbable in 

 this tradition, but we may observe, with Delambre, 2 that we are not 

 informed whether this new star remained in the sky, or soon disap- 

 peared again. Ptolemy makes no mention of the star or the story ; 

 and his catalogue contains no bright star which is not found in the 

 " Catasterisms" of Eratosthenes. These Catasterisms were an enumer- 

 ation of 475 of the principal stars, according to the constellations in 

 which they are, and were published about sixty years before Hip- 

 parchus. 



2. Constant Length of Years. Hipparchus also attempted to ascer- 

 tain whether successive years are all of the same length ; and though, 

 with his scrupulous love of accuracy, 3 he does not appear to have 



fiat. Hist. lib. ii. (xxvi.) > A. A. i. 290. 3 Ptolem. Synt. iii. 



