Babylonian astronomy and astrology

Mesopotamian knowledge

Babylonian astronomy dates from the 9th century BC. This immense culture reached us thanks to thousands of clay tablets engraved with a stylus (a small part concerns astronomy).
The historians of science consider that Mesopotamian astronomy was not a science, because of the preponderant place of astrology. However astrology and astronomy in Mesopotamia are part of the same field of thought, the same form of celestial knowledge or "astral science".
The oldest data we know comes from the Babylonians who lived in Mesopotamia 4000 years ago.
The phenomena measured in priority were the rising and setting of the stars (first and last visibilities in the sky). But also the synodic periods (duration to return to the same celestial configuration).
In addition, many regular celestial phenomena of astronomy are noted. Among these data we find the eclipses of the Moon, of the Sun, the changes of lunar phase, the periods of Mercury, of Venus, of Mars, of Jupiter, of Saturn, the inclination of the Earth's orbit, the oppositions and the conjunctions planets.
The reference point for celestial observations was the horizon.
Mesopotamian astrology consisted in noting the periodicity of certain celestial phenomena in order to identify if their appearances and disappearances were following their normal course. If the phenomenon was regular, the omen was positive. Whether the phenomenon was early or late, the omen was negative.
The distribution of stars in the sky and the movements of wandering stars (synodic period) were known in the first half of the 1st millennium BC. AD
It was on these bases that several reference systems had been developed, including the zodiacal system.
From the 5th century BC. J.-C, the ecliptic is divided into 12 sections of 30 degrees containing the 12 constellations corresponding approximately to our signs of the current zodiac.
The zodiac has been a reference system in almanacs (calendars showing major dates), horoscopes (examination of the time of a birth in relation to celestial events) and ephemeris (astronomical tables by which we determine, for each day, the positions of the planets). Babylonian horoscopes date from 410 BC. J.-C.

Example of a child's birth horoscope:
“In the year 243, in the month of Nisannu, on the 20th day (April 16, 69 BC), during the 9th hour, a child is born. At this time, the Moon was in the end of Capricorn at 18°, the Sun in the end of Aries at 30°, Jupiter in Sagittarius at 24°, Venus in Gemini at 13°, Saturn in Aquarius at 15° , Mars in Libra at 14°, Mercury which had not risen was not visible. The moonset before sunrise occurred on the 14th day, the last lunar visibility occurred on the 27th day. That year on the 28th day of the month Abu (August 20, 69 BC), an expected solar eclipse was not observed at the end of Leo. On the 13th day of the month Ululu (September 3, 69 BC) at sunset a lunar eclipse exceeding one third of the disk occurred; the Moon was already eclipsed when it rose in Pisces. The good fortune of this child... "
One of the main contributions of regular observations was the empirical measurement of the cycles of the Moon and the Sun, essential for the determination of calendars although these already had a long history. Ancient calendars were based on empirical observation of the cycles of the Moon and the Sun. The so-called "lunisolar" system had a year of 12 months (cycle of the Moon). This made it possible to predict when she would reappear in Heaven. In this context, the month is 29 or 30 days (on average the synodic month is about 29 and a half days).
At the end of the 4th millennium BC. AD, the month lasted 30 days and the year lasted 12 months. It is this simplified reference which was used to carry out calculations. Then we adjusted in relation to the actual length of the year observed.
Since the 3rd millennium BC. AD to correct the difference between the calculation and the observation, we added empirically, an intercalary month.
Babylonian astrology and astronomy were the source of Greek, Byzantine, Syrian, medieval astronomy of Muslims and Europeans.
Classical Greek and Latin sources frequently refer to Mesopotamian astronomers as "Chaldeans," often to present them as scholars of astrology and other forms of divination.

NB: the Babylonian ephemeris were translated in the 19th century.

Image: Babylonia (southern Iraq). Babylonian civilization flourished in Southern Mesopotamia. It continues from the beginning of the 2nd millennium BC. AD until the beginning of our era. It comes from the older civilizations of Mesopotamia (Sumer and Akkad).

Image: The constellations of the Mesopotamian "zodiac".