Astronomy began with the first settlements of agricultural societies. Mesopotamia, the land between the Tigris and Euphrates rivers in what is today Iraq, was the birthplace of civilization almost 10,000 years ago. It is in ancient Sumeria that we find the oldest records of the study of astronomy. Babylon and Assyria were later civilizations in the same geographic area, and inherited the Sumerians' astronomical traditions and many of their myths and legends surrounding the skies. They in turn developed their own astronomical culture and passed it on to the Greeks and eventually to our modern world. Perhaps the greatest legacy to modern western astronomy was left to us by the Babylonians. We still use many of their original constellations, and the records they kept of astronomical occurences allow us a glimpse into their view of the heavens.
Purposes of Astronomy in Ancient Mesopotamian Civilization
As in most ancient cultures, astronomy was actually practiced as astrology. Astronomical events, whether they were every-day occurences or rare incidents, had a deep religious meaning for the people. It was believed that all things happened for a reason. This spiritual angle often spilled over onto the social or political levels as well. Kings and nobles relied heavily on omens which were witnessed and interpreted by a powerful group of priest-astronomers. Lives were lived according to the advice of these astronomers, who seemingly were able to understand the universe and make predications based on their observations.
A great deal of astronomical mythology was handed down from the Sumerians. Constellations that we still use today, such as Leo, Taurus, Scorpius, Auriga, Gemini, Capricorn, and Sagittarius, were invented by the Sumerians and Babylonians between 2000-3000 B.C. These constellations had mythical origins, the stories of which are common throughout the western world. The Babylonians created a zodiac, which marked the twelve constellations that the sun, moon, and planets travel between during their movements through the sky.
However, besides being the manifestation of legends, the constellations provided a practical use for the people of ancient Mesopotamia. Like in other societies, the orientation of the constellations was used to mark seasons for harvesting or sowing crops. Certain constellations were noted for their yearly rising or setting times, and provided an accurate clock by which time could be measured. The Babylonians kept written records of calendars used for planting.
Babylonians kept records on clay tablets using a type of writing called cuneiform. At first this was generally for business purposes, in order to keep track of financial transactions and inventories. Several cuneiform tablets have been found, however, that focus on more scientific topics. One notable example is the Venus Tablet of King Ammizaduga, pictured below, which demonstrates the scientific methodology used by the Babylonian astronomers. The main topic of this tablet is the appearance and disappearance of the planet Venus as it goes from being an evening star to a morning star. Based on the detailed astronomical patterns mentioned in this tablet, modern scientists were able to use computers to determine that the Venus tablet was probably written in the year 1581 B.C. Another astronomical cuneiform tablet was found in the tomb of King Ashurbanipal of Ninevah, and also details the times of Venus' appearance and disappearance from the horizon.
The Babylonians not only recognized Venus as the same object whether it appeared in the morning or evening, but they actually developed a method for calculating the length of the Venus cycle! According to the Babylonians, the length of one cycle was 587 days, compared with the actual value of 584 days. The slight difference is due to the fact that they attempted to coincide these astronomical cycles with phases of the moon.
Both the Babylonians and the Assyrians were able to predict lunar eclipses. They applied a simple method which made future predictions based on past observations. Several cuneiform tablets list series of lunar eclipses and mark time between successive events.
One of the major breakthroughs of the Babylonians was their invention of the degree system to distinguish positions in the sky. The system was similar to our use of degrees to calculate latitude and longitude. The Greeks adopted the degree system and also many of the Babylonian constellations, which they renamed in Greek.
REFERENCES FOR THIS PAGE:
Anthony Aveni, Stairways to the Stars, John Wiley & Sons, 1997.
J. Norman Lockyer, The Dawn of Astronomy, MIT Press, 1894.