Coming down to times when astronomy had so far advanced that a catalogue of the stars had been drawn up, with their positions determined by actual measurement, it became possible for astrologers to draw up something like a definite system of prediction, based upon the constellations or parts of a constellation that happened to be rising at any given moment, and this was the system employed when Zeuchros of Babylon wrote in the first century of our era. His system must have been started later than 700 B.C., for in it Aries is considered as the leader of the zodiac; the constellations are already disestablished in favour of the Signs; and the Signs are each divided into three. A practical drawback to this particular astrological system was that the aspect presented by the heavens on one evening was precisely the same as that presented on the next evening four minutes earlier. The field for prediction therefore was very limited and repeated itself too much for the purpose of fortune-tellers. The introduction of the planets into astrology gave a greater diversity to the material used by the fortune-tellers. An early phase of planetary astrology consisted in the allotment of a planet to each hour of the day and also to each day of the week. It has been already shown in the chapter on "Saturn and Astrology," that this system arose from the Ptolemaic idea of the solar system grafted on the Egyptian division of the day into twenty-four hours, and applied to the week of seven days. It probably originated in Alexandria, and arose not earlier than the third century before our era. Mathematical astrology--the complex system now in vogue--involves a considerable knowledge of the apparent movements of the planets and a development of mathematics such as did not exist until the days of Hipparchus. It also employs the purely imaginary signs of the zodiac, not the constellations; and reckons the first point of Aries as at the spring equinox. So far as we can ascertain, the spring equinox marked the first point of the constellation Aries about B.C. 110. All these varied forms of astrology are therefore comparatively recent. Before that it was of course reckoned ominous if an eclipse took place, or a comet was seen, or a bright planet came near the moon, just as spilling salt or crossing knives may be reckoned ominous to-day. The omens had as little to do with observation, or with anything that could be called scientific, in the one case as in the other. It is important to realize that astrology, as anything more than the crude observance of omens, is younger than astronomy by at least 2,000 years.