Babylonian Astronomy
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Babylonian Astronomy
Babylonian astronomy refers to the astronomy that developed in Mesopotamia, the "land
between the rivers" Tigris and Euphrates, corresponding to modern-day Iraq, where the
ancient kingdoms of Sumer, Akkad, Assyria, Babylonia and Chaldea were located.
Babylonian astronomy was the basis for much of the astronomical traditions that later
developed in Greek and Hellenistic astronomy, in classical Indian astronomy, in Sassanid,
Byzantine and Syrian astronomy, in medieval Islamic astronomy, and in Western European
astronomy.
The origins of Western astronomy can be found in Mesopotamia.
A form of writing known as cuneiform emerged among the Sumerians around 3500-3000 BC.
The Sumerians only practiced a basic form of astronomy, but they had an important
influence on the sophisticated astronomy of the Babylonians.
Astral theology, which gave planetary gods an important role in Mesopotamian mythology
and religion, began with the Sumerians. They also used a sexagesimal (base 60) place-value
number system, which simplified the task of recording very large and very small numbers.
The modern practice of dividing a circle into 360 degrees, of 60 minutes each, began with the Sumerians. For more information, see the articles on Babylonian numerals and mathematics.
During the 8th and 7th centuries BC, Babylonian astronomers developed a new empirical approach
to astronomy. They began studying philosophy dealing with the ideal nature of the early universe
and began employing an internal logic within their predictive planetary systems. This was an
important contribution to astronomy and the philosophy of science, and some scholars have thus referred to this new approach as the first scientific revolution.
This new approach to astronomy was adopted and further developed in Greek and Hellenistic
astronomy.
Classical Greek and Latin sources frequently use the term Chaldeans for the astronomers of Mesopotamia, who were, in reality, priest-scribes specializing in astrology and other forms of
divination.
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Old Babylonian Astronomy
Old Babylonian astronomy refers to the astronomy that was practiced during and after the First Babylonian Dynasty and before the Neo-Babylonian Empire.
The first evidence of recognition that astronomical phenomena are periodic and of the application
of mathematics to their prediction is Babylonian.
Tablets dating back to the Old Babylonian period document the application of mathematics to
the variation in the length of daylight over a solar year. Centuries of Babylonian observations of
celestial phenomena are recorded in the series of cuneiform tablets known as the Enūma Anu Enlil.
The oldest significant astronomical text that we possess is Tablet 63 of the Enūma Anu Enlil, the
Venus tablet of Ammi-saduqa, which lists the first and last visible risings of Venus over a period
of about 21 years and is the earliest evidence that the phenomena of a planet were recognized
as periodic.
The MUL.APIN, contains catalogues of stars and constellations as well as schemes for predicting
heliacal risings and the settings of the planets, lengths of daylight measured by a water clock,
gnomon, shadows, and intercalations. The Babylonian GU text arranges stars in 'strings' that lie
along declination circles and thus measure right-ascensions or time-intervals, and also employs
the stars of the zenith, which are also separated by given right-ascensional differences.
There are dozens of cuneiform Mesopotamian texts with real observations of eclipses, mainly
from Babylonia (see Wikipedia's relevant page, "Chronology of Babylonia and Assyria").
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Neo-Babylonian Astronomy
Neo-Babylonian Astronomy refers to the astronomy developed by Chaldean astronomers during
the Neo-Babylonian, Seleucid and Parthian periods of Mesopotamian history.
A significant increase in the quality and frequency of Babylonian observations appeared during
the reign of Nabonassar (747-733 BC), who founded the Neo-Babylonian Empire.
The systematic records of ominous phenomena in astronomical diaries that began at this time
allowed for the discovery of a repeating 18-year cycle of lunar eclipses, for example.
The Egyptian astronomer Ptolemy later used Nabonassar's reign to fix the beginning of an era,
since he felt that the earliest usable observations began at this time.
The last stages in the development of Babylonian astronomy took place during the time of the
Seleucid Empire (323-60 BC).
In the third century BC, astronomers began to use "goal-year texts" to predict the motions of
the planets. These texts compiled records of past observations to find repeating occurrences
of ominous phenomena for each planet. About the same time, or shortly afterwards, astronomers created mathematical models that allowed them to predict these phenomena directly, without
consulting past records.
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Empirical Astronomy
Most of the Chaldean astronomers were concerned exclusively with ephemerides, and not with
theory. The predictive Babylonian planetary models were usually strictly empirical and arithme-
tical, and usually did not involve geometry, cosmology or speculative philosophy like that of
the later Hellenistic models, though the Babylonian astronomers were concerned with philoso-
phy dealing with the ideal nature of the early universe.
Contributions made by the Chaldean astronomers during this period include the discovery of
eclipse cycles and saros cycles, and many accurate astronomical observations.
Chaldean astronomers known to have followed this model include Naburimannu (fl. 6th-3rd
century BC), Kidinnu (d. 330 BC), Berossus (3rd century BC), and Sudines (fl. 240 BC).
They are known to have had a significant influence on the Greek astronomer Hipparchus and
the Egyptian astronomer Ptolemy, as well as other Hellenistic astronomers.
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Heliocentric Astronomy
The only Babylonian astronomer known to have supported a heliocentric model of planetary
motion was Seleucus of Seleucia (b. 190 BC).[7][8][9] Seleucus is known from the writings
of Plutarch. He supported the heliocentric theory where the Earth rotated around its own
axis which in turn revolved around the Sun.
According to Plutarch, Seleucus even proved the heliocentric system, but it is not known
what arguments he used.
According to Lucio Russo, his arguments were probably related to the phenomenon of tides.
Seleucus correctly theorized that tides were caused by the Moon, although he believed that
the interaction was mediated by the Earth's atmosphere. He noted that the tides varied in
time and strength in different parts of the world.
According to Strabo (1.1.9), Seleucus was the first to state that the tides are due to the
attraction of the Moon, and that the height of the tides depends on the Moon's position
relative to the Sun.
According to Bartel Leendert van der Waerden, Seleucus may have proved the heliocentric
theory by determining the constants of a geometric model for the heliocentric theory and
by developing methods to compute planetary positions using this model. He may have used trigonometric methods that were available in his time, as he was a contemporary of
Hipparchus.
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