A Crash Course In Mesopotamian Astronomy

The Mesopotamians had an established understanding of basic astronomy. 5000 years ago, the Babylonians and Egyptians grouped the stars into constellations, realising that their predictable movements could serve as indicators for navigational, agricultural and time keeping purposes. In 2000 BC, Babylonian priests recorded the motions of planets on thousands of clay tablets. Both the Babylonians and the Egyptians identified the Sun's yearly path through the constellations, and incorporated this along with their knowledge of the movement of the moons and planets into a system of astrology with a 12 sign-zodiac. By 200 BC the Babylonians were predicting lunar eclipses and some solar eclipses.

While the Chaldeans did less with astronomy than the Babylonians, they discovered a method of predicting, within a certain degree of accuracy, the apparent motion of the planets as they sped through the sky, along with times of retrograde (backwards) motion, helical rising and setting, and conjunctions with principal stars.

The Mesopotamians recognized the precession of the equinox. They observe that the vernal equinox shifts westward by 50" anually and attributed it to Earth's equatorial bulge attracted gravitationally by Sun and Moon. They noted the phases, rotation and revolution period of the moon and planet synodic and sidereal periods.

Around 1000BC the astronomical knowledge of the Babylonians was passed to the Greeks, who identified 48 constellations. Today we have 88 groups of stars. Unlike their precessors, the Greeks sought geometrical explanations of motion rather than the numerical relationships the Babylonians used in tabulated observations. As a result, the Greeks made more progress in astronomy than the other Mesopotamians, who moved slowly away from pure science into vernacular astrology.

One of the principal stars in Mesopotamian religion and astronomy was Venus, embodified by the goddess Ishtar to the Babylonians and Assyrians, Astarte to the Phoenicians, Athtar in Arabia, Astar in Abyssinia (now Ethiopia), and Ashtart in Canaan and Israel. As Ishtar of Erech (in Babylonia)she was worshipped in connection with the evening star, while as Ishtar of Akkad (also in Babylonia) she was identified with the morning star. Ishtar was called "the eldest of heaven and earth", and daughter of Anu, the god of heaven. She was the goddess of love and beauty, the "Great Mother", and to the Assyrians, a goddess of hunting and war.

The earliest formal calendar in Mesopotamia was probably the Sumerian lunar calendar which influenced the calendar systems of other cultures. Since the lunar calendar required intercalation (insertion of days or other portions of time in calendars), the Babylonia calendar priests intercalated months according to an 8 year cycle when they would add 3 extra monts. The calendar months started with the direct observation of a new cresent moon at dusk. Today Judaism and Islâm calendars still use the principle that the new calendar day begins at sunset.

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