It must not be supposed, however, that the Chaldean astronomer had made any very extraordinary advances upon the knowledge of the Egyptian "watchers of the night." After all, it required patient observation rather than any peculiar genius in the observer to note in the course of time such broad astronomical conditions as the regularity of the moon's phases, and the relation of the lunar periods to the longer periodical oscillations of the sun. Nor could the curious wanderings of the planets escape the attention of even a moderately keen observer. The chief distinction between the Chaldean and Egyptian astronomers appears to have consisted in the relative importance they attached to various of the phenomena which they both observed. The Egyptian, as we have seen, centred his attention upon the sun. That luminary was the abode of one of his most important gods. His worship was essentially solar. The Babylonian, on the other hand, appears to have been peculiarly impressed with the importance of the moon. He could not, of course, overlook the attention-compelling fact of the solar year; but his unit of time was the lunar period of thirty days, and his year consisted of twelve lunar periods, or 360 days. He was perfectly aware, however, that this period did not coincide with the actual year; but the relative unimportance which he ascribed to the solar year is evidenced by the fact that he interpolated an added month to adjust the calendar only once in six years. Indeed, it would appear that the Babylonians and Assyrians did not adopt precisely the same method of adjusting the calendar, since the Babylonians had two intercular months called Elul and Adar, whereas the Assyrians had only a single such month, called the second Adar.[8] (The Ve'Adar of the Hebrews.) This diversity further emphasizes the fact that it was the lunar period which received chief attention, the adjustment of this period with the solar seasons being a necessary expedient of secondary importance. It is held that these lunar periods have often been made to do service for years in the Babylonian computations and in the allied computations of the early Hebrews. The lives of the Hebrew patriarchs, for example, as recorded in the Bible, are perhaps reckoned in lunar "years." Divided by twelve, the "years" of Methuselah accord fairly with the usual experience of mankind.

Yet, on the other hand, the convenience of the solar year in computing long periods of time was not unrecognized, since this period is utilized in reckoning the reigns of the Assyrian kings. It may be added that the reign of a king "was not reckoned from the day of his accession, but from the Assyrian new year's day, either before or after the day of accession. There does not appear to have been any fixed rule as to which new year's day should be chosen; but from the number of known cases, it appears to have been the general practice to count the reigning years from the new year's day nearest the accession, and to call the period between the accession day and the first new year's day 'the beginning of the reign,' when the year from the new year's day was called the first year, and the following ones were brought successively from it. Notwithstanding, in the dates of several Assyrian and Babylonian sovereigns there are cases of the year of accession being considered as the first year, thus giving two reckonings for the reigns of various monarchs, among others, Shalmaneser, Sennacherib, Nebuchadrezzar."[9] This uncertainty as to the years of reckoning again emphasizes the fact that the solar year did not have for the Assyrian chronology quite the same significance that it has for us.

The Assyrian month commenced on the evening when the new moon was first observed, or, in case the moon was not visible, the new month started thirty days after the last month. Since the actual lunar period is about twenty-nine and one-half days, a practical adjustment was required between the months themselves, and this was probably effected by counting alternate months as Only 29 days in length. Mr. R. Campbell Thompson[10] is led by his studies of the astrological tablets to emphasize this fact. He believes that "the object of the astrological reports which related to the appearance of the moon and sun was to help determine and foretell the length of the lunar month." Mr. Thompson believes also that there is evidence to show that the interculary month was added at a period less than six years. In point of fact, it does not appear to be quite clearly established as to precisely how the adjustment of days with the lunar months, and lunar months with the solar year, was effected. It is clear, however, according to Smith, "that the first 28 days of every month were divided into four weeks of seven days each; the seventh, fourteenth, twenty-first, twenty-eighth days respectively being Sabbaths, and that there was a general prohibition of work on these days." Here, of course, is the foundation of the Hebrew system of Sabbatical days which we have inherited. The sacredness of the number seven itself - the belief in which has not been quite shaken off even to this day - was deduced by the Assyrian astronomer from his observation of the seven planetary bodies - namely, Sin (the moon), Samas (the sun), Umunpawddu (Jupiter), Dilbat (Venus), Kaimanu (Saturn), Gudud (Mercury), Mustabarru-mutanu (Mars).[11] Twelve lunar periods, making up approximately the solar year, gave peculiar importance to the number twelve also. Thus the zodiac was divided into twelve signs which astronomers of all subsequent times have continued to recognize; and the duodecimal system of counting took precedence with the Babylonian mathematicians over the more primitive and, as it seems to us, more satisfactory decimal system.

Another discrepancy between the Babylonian and Egyptian years appears in the fact that the Babylonian new year dates from about the period of the vernal equinox and not from the solstice. Lockyer associates this with the fact that the periodical inundation of the Tigris and Euphrates occurs about the equinoctial period, whereas, as we have seen, the Nile flood comes at the time of the solstice. It is but natural that so important a phenomenon as the Nile flood should make a strong impression upon the minds of a people living in a valley. The fact that occasional excessive inundations have led to most disastrous results is evidenced in the incorporation of stories of the almost total destruction of mankind by such floods among the myth tales of all peoples who reside in valley countries. The flooding of the Tigris and Euphrates had not, it is true, quite the same significance for the Mesopotamians that the Nile flood had for the Egyptians. Nevertheless it was a most important phenomenon, and may very readily be imagined to have been the most tangible index to the seasons. But in recognizing the time of the inundations and the vernal equinox, the Assyrians did not dethrone the moon from its accustomed precedence, for the year was reckoned as commencing not precisely at the vernal equinox, but at the new moon next before the equinox.