Several centuries before Hipparchus was born, the Assyrian kings had in their palaces official astronomers who were able to foretell, with varying degrees of accuracy, when eclipses would take place.  Instructions were sent to various observatories, in the king’s name, to send in reports of forthcoming eclipses.  A translation of one of these official documents sent from the observatory of Babylon to Nineveh, has been published by Professor Harper.  The following are extracts from it:  “As for the eclipse of the moon about which the king my lord has written to me, a watch was kept for it in the cities of Akkad, Borsippa, and Nippur.  We observed it ourselves in the city of Akkad....  And whereas the king my lord ordered me to observe also the eclipse of the sun, I watched to see whether it took place or not, and what passed before my eyes I now report to the king my lord.  It was an eclipse of the moon that took place....  It was total over Syria, and the shadow fell on the land of the Amorites, the land of the Hittites, and in part on the land of the Chaldees.”  Professor Sayce comments:  “We gather from this letter that there were no less than three observatories in Northern Babylonia:  one at Akkad, near Sippara; one at Nippur, now Niffer; and one at Borsippa, within sight of Babylon.  As Borsippa possessed a university, it was natural that one of the three observatories should be established there."[349]

It is evident that before the astronomers at Nineveh could foretell eclipses, they had achieved considerable progress as scientists.  The data at their disposal probably covered nearly two thousand years.  Mr. Brown, junior, calculates that the signs of the Zodiac were fixed in the year 2084 B.C.[350] These star groups do not now occupy the positions in which they were observed by the early astronomers, because the revolving earth is rocking like a top, with the result that the pole does not always keep pointing at the same spot in the heavens.  Each year the meeting-place of the imaginary lines of the ecliptic and equator is moving westward at the rate of about fifty seconds.  In time—­ages hence—­the pole will circle round to the point it spun at when the constellations were named by the Babylonians.  It is by calculating the period occupied by this world-curve that the date 2084 B.C. has been arrived at.

As a result of the world-rocking process, the present-day “signs of the Zodiac” do not correspond with the constellations.  In March, for instance, when the sun crosses the equator it enters the sign of the Ram (Aries), but does not reach the constellation till the 20th, as the comparative table shows on p. 308.

When “the ecliptic was marked off into the twelve regions” and the signs of the Zodiac were designated, “the year of three hundred sixty-five and one-fourth days was known”, says Goodspeed, “though the common year was reckoned according to twelve months of thirty days each[351], and equated with the solar year by intercalating a month at the proper times....  The month was divided into weeks of seven days....  The clepsydra and the sundial were Babylonian inventions for measuring time."[352]