astrology and astronomy

   Today, astronomy is the serious study of the universe and how it works, and astrology is considered a false science that claims that the movements of celestial objects directly affect life on Earth. The ancient Mes-opotamians did not make such distinctions between the two disciplines, however. Their observations of the heavens were made mainly to discern how the movements of the stars and planets affected earthly events. Because these bodies were seen as divine or divinely inspired objects, Mesopotamian astronomy also had a strong religious dimension.

   All of the Mesopotamian peoples observed the heavens, but the Babylonians, Assyrians, and Persians were particularly meticulous and often ingenious in their methods. Their "astronomers" were specially trained scribes. These men used hollow tubes as viewfinders and water clocks to time the risings and settings of stars and planets, Venus's disappearance behind the Sun and subsequent reappearance, and other celestial movements. The data thus collected was frequently recorded on clay tablets and kept in archives. The earliest surviving examples date from circa 1700 b.c., and many were discovered in the great library of the Assyrian king Ashurbanipal at Nineveh. Of particular importance today are the so-called Venus tablets, compiled by the astronomers of the Babylonian king Ammi-saduqa (reigned 1646 - 1626 b.c.). The observations recorded on the tablets were originally used to determine omens that might affect that monarch, but modern scholars use them to help date Mesopotamian events.

   Surviving records of the Mesopota-mian astronomers indicate that they paid close attention to unusual heavenly phenomena, such as lunar and solar eclipses and halos around the Sun. This is not surprising since the rarer and more dramatic celestial events were viewed as most likely to represent divine omens. Eventually these observers were able to predict eclipses with considerable accuracy. But observations of the regular, mundane movements of the Sun, the Moon, and the planets were also seen as important. Repeated observations of the Moon's movements, for instance, led to the introduction of a fairly accurate lunar calendar by the seventh century b.c. The year was thus divided into twelve lunar months, each of which corresponded to one of twelve constellations in the sky. These star groups, which were associated with various gods and mythical characters, made up the zodiac, which was firmly established by the early Persian period (ca. 400s b.c.) but probably existed earlier. About a century or two later, in the Seleucid period, horoscopes based on the signs of the zodiac were introduced.

   Regular observations of the movements of celestial objects also allowed Mes-opotamian astronomers to develop useful methods of and units for reckoning time, including hours and minutes. The Babylonians divided an hour into sixty minutes and counted twelve "double hours" in each day. (Greek astronomers later divided these into twenty-four single hours, creating the system familiar today.) Likewise, the Babylonian astronomer Kidenas (or Kidinnu) calculated the length of the solar year with an error of only about four minutes.

   In general, the Mesopotamian astronomers were just as bright and diligent as their Greek counterparts, who established the true science of astronomy between the sixth and third centuries b.c. The main difference was that the Greeks saw the heavenly bodies as lifeless objects following natural laws rather than as being divinely inspired; also, the Greeks incorporated their celestial observations into scientific theories in an effort to explain how the universe works.

   See also: Ammi-saduqa; Greeks; mathematics