Note 554 — Chapter XIX · ASSYRIANS. — BABYLON.

The earliest Chaldæan astronomical observation, known to the astronomer Ptolemy, both precise and of ascertained date to a degree sufficient for scientific use, was a lunar eclipse of the 19th March 721 B. C.—the 27th year of the era of Nabonassar (Ideler, Ueber die Astronomischen Beobachtungen der Alten, p. 19, Berlin, 1806). Had Ptolemy known any older observations conforming to these conditions, he would not have omitted to notice them: his own words in the Almagest testify how much he valued the knowledge and comparison of observations taken at distant intervals (Almagest, b. 3, p. 62, ap. Ideler, l. c. p. 1), and at the same time imply that he had none more ancient than the era of Nabonassar (Alm. iii, p. 77, ap. Idel. p. 169).

That the Chaldæans had been, long before this period, in the habit of observing the heavens, there is no reason to doubt; and the exactness of those observations cited by Ptolemy implies (according to the judgment of Ideler ib. p. 167) long previous practice. The period of two hundred and twenty-three lunations, after which the moon reverts nearly to the same positions in reference to the apsides and nodes, and after which eclipses return nearly in the same order and magnitude, appears to have been discovered by the Chaldæans (“Defectus ducentis viginti tribus mensibus redire in suos orbes certum est,” Pliny, H. N. ii, 13), and they deduced from hence the mean daily motions of the moon with a degree of accuracy which differs only by four seconds from modern lunar tables (Geminus, Isagoge in Arati Phænomena, c. 15; Ideler, l. c. pp. 153, 154, and in his Handbuch der Chronologie, vol. i, Absch. ii, p. 207).

There seem to have been Chaldæan observations, both made and recorded, of much greater antiquity than the era of Nabonassar; though we cannot lay much stress on the date of 1903 years anterior to Alexander the Great, which is mentioned by Simplicius (ad Aristot. de Cœlo, p. 123) as being the earliest period of the Chaldæan observations sent from Babylon by Kallisthenês to Aristotle. Ideler thinks that the Chaldæan observations anterior to the era of Nabonassar were useless to astronomers from the want of some fixed era, or definite cycle, to identify the date of each of them. The common civil year of the Chaldæans had been from the beginning (like that of the Greeks) a lunar year, kept in a certain degree of harmony with the sun by cycles of lunar years and intercalation. Down to the era of Nabonassar, the calender was in confusion, and there was nothing to verify either the time of accession of the kings, or that of astronomical phenomena observed, except the days and months of this lunar year. In the reign of Nabonassar, the astronomers at Babylon introduced (not into civil use, but for their own purposes and records) the Egyptian solar year,—of three hundred and sixty-five days, or twelve months of thirty days each, with five added days, beginning with the first of the month Thoth, the commencement of the Egyptian year,—and they thus first obtained a continuous and accurate mode of marking the date of events. It is not meant that the Chaldæans then for the first time obtained from the Egyptians the knowledge of the solar year of three hundred and sixty-five days, but that they then for the first time adopted it in their notation of time for astronomical purposes, fixing the precise moment at which they began. Nor is there the least reason to suppose that the era of Nabonassar coincided with any political revolution or change of dynasty. Ideler discusses this point (pp. 146-173, and Handbuch der Chronol. pp. 215-220). Syncellus might correctly say—Ἀπὸ Ναβονασάρου τοὺς χρόνους τῆς τῶν ἄστρων παρατηρησέως Χαλδαῖοι ἠκρίβωσαν (Chronogr. p. 207).

We need not dwell upon the back reckonings of the Chaldæans for periods of 720,000, 490,000, 470,000 years, mentioned by Cicero, Diodorus, and Pliny (Cicero, De Divin. ii, 46; Diod. ii, 31; Pliny, H. N. vii, 57), and seemingly presented by Berosus and others as the preface of Babylonian history.

It is to be noted that Ptolemy always cited the Chaldæan observations as made by “the Chaldæans,” never naming any individual; though in all the other observations to which he alludes, he is very scrupulous in particularizing the name of the observer. Doubtless he found the Chaldæan observations registered just in this manner; a point which illustrates what is said in the text respecting the collective character of their civilization, and the want of individual development or prominent genius.

The superiority of the Chaldæan priests to the Egyptian, as astronomical observers, is shown by the fact that Ptolemy, though living at Alexandria, never mentions the latter as astronomers, and cites no Egyptian observations while he cites thirteen Chaldæan observations in the years B. C. 721, 720, 523, 502, 491, 383, 382, 245, 237, 229: the first ten being observations of lunar eclipses; the last three, of conjunctions of planets and fixed stars (Ideler, Handbuch der Chronologie, vol. i, Ab. ii, pp. 195-199).