Astronomy. — ''The Ongin of the Saros". By Dr. A. Pannekoek. 

 (Communicated by Prof. W. Dk Sitter). 



(Communicated in the meeting of September 29, 1917). 



The forecast of eclipses, which to the uneducated is such a con- 

 vincing proof of the power and accuracy of astronomical science, 

 is not the fruit of the highly developed modern theory, but belongs 

 to the oldest products of human science. Greek writers tell us that 

 the Babylonians were already able to predict the eclipses by means 

 of a period of 18 years, which they called "saros", and which rested 

 on the fact that 223 synodic hmar periods and 242 di-aconic revo- 

 lutions are practically equal (both 658573 days), that after this 

 period, therefore, full and new moon return to the same position 

 relatively to the nodes. 



When at a later period this meaning of the saros as common 

 multiple of two lunar periods was once grasped, the saros itself 

 was no longer necessary, and the eclipses could be calculated directly 

 from the knowledge of the orbits of sun and moon. But tliis 

 scientific height was reached in Seleucidic Babylon and in Greece 

 only in the last centuries B. C. The origin of the use of the saros 

 falls in earlier times; and the tirst question is, what times? 



According to the theory of Hugo Winckler's school, Babylonian 

 astronomy had reached its highest perfection as early as 2000 — 

 3000 B. C, and therefore the origin of the saros lay in such a 

 far-off time that there is no possibility of following the road to the 

 discovery. But Kuglek's researches have proved this theory to be 

 to a large extent ungrounded romance. Afterwards, the last cham- 

 pion of the great antiquity of Babylonian astronomy, Ernst Weidner, 

 tried to prove that the saros must have been known at least 1000 

 B. C, but in this he was not successful '). Kugler's argument for 

 the opposite opinion is undoubtedly sound: 



"The most ancient Babylonian observations of lunar eclipses whicii 

 are in any way serviceable, date according to Ptolemy from the years 

 721 and 720 B. C. The accuracy found therein in no way exceeds 



1) E. Weidner, "Alter u. Bedeutung der babylonischen Astronomie u. Astral- 

 lehre" (1914) p. 16. See also F. X. Kugler, "Sternkunde u. Sterndienst in Babel. 

 Erganzungen" p. 241. 



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