The Babylonians called the Zodiacal constellations the “Houses of the Sun,” and distinguished from them another set of asterisms, which they denominated the “Houses of the Moon.” As the Sun and Moon both move through the sky in nearly the same plane, the path of the Moon merely crossing and recrossing that of the Sun, but never diverging from it further than a few degrees, it would seem that these “Houses of the Moon,” or lunar asterisms, must have been a division of the Zodiacal stars different from that employed with respect to the sun, either in the number of the “Houses,” or in the point of separation between “House” and “House.”
The Babylonians observed and calculated eclipses; but their power of calculation does not seem to have been based on scientific knowledge, nor to have necessarily implied sound views as to the nature of eclipses or as to the size, distance, and real motions of the heavenly bodies. The knowledge which they possessed was empirical. Their habits of observation led them to discover the period of 223 lunations or 18 years 10 days, after which eclipses—especially those of the the moon—recur again in the same order. Their acquaintance with this cycle would enable them to predict lunar eclipses with accuracy for many ages, and solar eclipses without much inaccuracy for the next cycle or two.
That the Babylonians carefully noted and recorded eclipses is witnessed by Ptolemy, who had access to a continuous series of such observations reaching back from his own time to B.C. 747. Five of these—all eclipses of the moon—were described by Hipparchus from Babylonian sources, and are found to answer all the requirements of modern science. They belong to the years B.C. 721, 720, 621, and 523. One of them, that of B.C. 721, was total at Babylon. The others were partial, the portion of the moon obscured varying from one digit to seven.
There is no reason to think that the observation of eclipses by the Babylonians commenced with Nabonassar. Ptolemy indeed implies that the series extant in his day went no higher; but this is to be accounted for by the fact, which Berosus mentioned, that Nabonassar destroyed, as far as he was able, the previously existing observations, in order that exact chronology might commence with his own reign.
Other astronomical achievements of the Babylonians were the following. They accomplished a catalogue of the fixed stars, of which the Greeks made use in compiling their stellar tables. They observed and recorded their observations upon occultations of the planets by the sun and moon. They invented the gnomon and the polos, two kinds of sundial, by means of which they were able to measure time during the day, and to fix the true length of the solar day, with sufficient accuracy. They determined correctly within a small fraction the length of the synodic revolution of the moon. They knew that the true length of the solar year was 365 days and a quarter, nearly. They noticed comets, which they believed to be permanent bodies, revolving in orbits like those of the planets, only greater. They ascribed eclipses of the sun to the interposition of the moon between the sun and the earth. They had notions not far from the truth with respect to the relative distance from the earth of the sun, moon, and planets. Adopting, as was natural, a geocentric system, they decided that the Moon occupied the position nearest to the earth; that beyond the Moon was Mercury, beyond Mercury Venus, beyond Venus Mars, beyond Mars Jupiter, and beyond Jupiter, in the remotest position of all, Saturn. This arrangement was probably based upon a knowledge, more or less exact, of the periodic times which the several bodies occupy in their (real or apparent) revolutions. From the difference in the times the Babylonians assumed a corresponding difference in the size of the orbits, and consequently a greater or less distance from the common centre.
Thus far the astronomical achievements of the Babylonians rest upon the express testimony of ancient writers—a testimony confirmed in many respects by the monuments already deciphered. It is suspected that, when the astronomical tablets which exist by hundreds in the British Museum come to be thoroughly understood, it will be found that the acquaintance of the Chaldaean sages with astronomical phenomena, if not also with astronomical laws, went considerably beyond the point at which we should place it upon the testimony of the Greek and Roman writers. There is said to be distinct evidence that they observed the four satellites of Jupiter, and strong reason to believe that they were acquainted likewise with the seven satellites of Saturn. Moreover, the general laws of the movements of the heavenly bodies seem to have been so far known to them that they could state by anticipation the position of the various planets throughout the year.
In order to attain the astronomical knowledge which they seem to have possessed, the Babylonians must undoubtedly have employed a certain number of instruments. The invention of sun-dials, as already observed, is distinctly assigned to them. Besides these contrivances for measuring time during the day, it is almost certain that they must have possessed means of measuring time during the night. The clepsydra, or water-clock, which was in common use among the Greeks as early as the fifth century before our era, was probably introduced into Greece from the East, and is likely to have been a Babylonian invention. The astrolabe, an instrument for measuring the altitude of stars above the horizon, which was known to Ptolemy, may also reasonably be assigned to them. It has generally been assumed that they were wholly ignorant of the telescope. But if the satellites of Saturn are really mentioned, as it is thought that they are, upon some of the tablets, it will follow—strange as it may seem to us—that the Babylonians possessed optical instruments of the nature of telescopes, since it is impossible, even in the clear and vapor-loss sky of Chaldaea, to discern the faint moons of that distant planet without lenses. A lens, it must be remembered, with a fair magnifying power, has been discovered among the Mesopotamian ruins. A people ingenious enough to discover the magnifying-glass would be naturally led on to the invention of its opposite. When once lenses of the two contrary kinds existed, the elements of a telescope were in being. We could not assume from these data that the discovery was made; but if it shall ultimately be substantiated that bodies invisible to the naked eye were observed by the Babylonians, we need feel no difficulty in ascribing to them the possession of some telescopic instrument.
The astronomical zeal of the Babylonians was in general, it must be confessed, no simple and pure love of an abstract science. A school of pure astronomers existed among them; but the bulk of those who engaged in the study undoubtedly pursued it in the belief that the heavenly bodies had a mysterious influence, not only upon the seasons, but upon the lives and actions of men—an influence which it was possible to discover and to foretell by prolonged and careful observation. The ancient writers, Biblical and other, state this fact in the strongest way; and the extant astronomical remains distinctly confirm it. The great majority of the tablets are of an astrological character, recording the supposed influence of the heavenly bodies, singly, in conjunction, or in opposition, upon all sublunary affairs, from the fate of empires to the washing of hands or the paring of nails. The modern prophetical almanac is the legitimate descendant and the sufficient representative of the ancient Chaldee Ephemeris, which was just as silly, just as pretentious, and just as worthless.
The Chaldee astrology was, primarily and mainly, genethlialogical. It inquired under what aspect of the heavens persons were born, or conceived, and, from the position of the celestial bodies at one or other of these moments, it professed to deduce the whole life and fortunes of the individual. According to Diodorus, it was believed that a particular star or constellation presided over the birth of each person, and thenceforward exercised over his life a special malign or benignant influence. But his lot depended, not on this star alone, but on the entire aspect of the heavens at a certain moment. To cast the horoscope was to reproduce this aspect, and then to read by means of it the individual’s future.