Ancient Babylonian Astronomy and the zodiac Calendar

Ancient Babylonian astronomy dates back to 1,800 BC and ultimately concerned itself in the establishment of an accurate calendar, the emphasis was on recording and calculating the motions of the Sun and Moon.

Babylonian temple astronomers called “tupsar Enuma Enlil” observed the skies for centuries and recorded their findings in astronomical diaries and star catalogues. Using these observations Babylonian astronomers had the ability to predict lunar and later solar eclipses with fairly precise accuracy. From Babylonian astronomy the Saros-cycle was developed. The Saros cycle is a period of 223 synodic months, or 18 years+11.3 days in reflection of the lunar and solar patterns.

The results of Babylonian astronomy predictions were also able to calculate that 235 lunar months are nearly identical to 19 solar years, with a difference of two hours. In conclusion to this observation, seven out of nineteen years should be leap years with an extra month.
Babylonian astronomy compiled detailed stellar catalogues becoming the principle of which we refer to as the Zodiac calendar.
Ancient Babylonian astronomy and astrological data records may have been motivated by religious reasoning. Such occurrences as a planets first and last appearance in the sky were taken to have astrological significance in foretelling human fate and destiny.

A Diary of Ancient Babylonian Astrology

A typical diary of ancient Babylonian astrology consists with a statement on the length of the previous month, followed by observations made for the current month. Details such as the time between sunset and moonset are given as well as intervals between the risings of the waxing moon.
When eclipses are recorded notice is given of the visible planets and their positions including the duration of the eclipse.

Significant attention is given to the appearances of Sirius in all recordings. The diaries of Ancient Babylonian astrology included details of atmospheric phenomena such as rainbows and halos, alongside various local events like fires and theft. Astrology was not studied as a personal aid, but for the benefit of the king and the land.

Ancient Babylonian astrology prediction and sexagesimal numbers

Calculations for accurate predictions were affected by use of the sexagesimal system of numbers. This system is still in use today. The sexagesimal system has a place value of 60 to measure time and angle. I.e. 60 seconds in a minute and 60 minutes in an hour. The ancient Babylonian sexagesimal system included dividing a circle into 360 degrees and the year into 12 parts.

The Ancient Babylonian Astronomy Calendar

Babylonian astronomy calculations and predictions evolved into a calendar. The Babylonian calendar is based on a lunar year.
There were 12 months in a lunar year. These months were much shorter than the months we know today, and often an extra month was added. A Babylonian year started with the spring equinox. As an example of how ancient Babylonian astrology worked for the people and their beliefs. The position of the sun and the moon in the sky during what we know as the spring equinox was a good omen for agriculture, a time for planting, then by calculation they were able to predict when the next good omen for agriculture should appear.

The names of the Babylonian months are in reflection of the names given to star constellations:

• Tashritu
• Arahsamna
• Kislimu
• Tebetu
• Sabatu
• Addaru
• Nisannu
• Aiaru
• Simanu
• Du'uzu
• Abu
• Alulu
• The extra month was called the second Elul.


The Babylonian people viewed celestial bodies as Gods. The planet Venus was the Goddess Ishtar, and Jupiter for example was the chief Babylonian god Marduk.




A Brief Chronological Study of Ancient Babylonian Astronomy.


Astronomers begin the old Babylonian period from circa 2000-1600 BCE when the Babylonian astronomers sought to master understanding of the duration of days and night, the rising and setting of the moon, and the appearance and disappearance of Venus.


The Kassite Period of Babylonian astrology begins from circa 1570-1160 BCE where attention was given to planetary and stellar risings and settings. Observations continued on daylight lengths. During this period Babylonian astronomers divided the moon into 4 equal sectors to represent 4 counties, Akkad, Sabartu, Elam, and Amurra.


Between 1400-900 BCE Exact observations of the heliacal risings of fixed stars were recorded. Ancient Babylonian astronomy developed a scheme of 34 heliacally rising stars and constellations that became associated with 12 calendar months. 1150 BCE saw the start of simple mathematical astronomy.


Astronomy history records 1000-600 BCE as the Late Assyrian Period where detailed studies of the fixed stars and their risings were established. Zodiacal constellations were established with recognition of the zodiac path of the moon, the sun, and the planets. The seasons of the year were established, and observations and predictions of eclipses were refined.


626-539 BCE is the Neo-Babylonian period, also called the Chaldean period.5. The Neo-Babylonian (Chaldean) Period (626-539 BCE). This period saw progress towards the division of the zodiac into 12 signs of 30 degrees each. 630 BCE was the start of the most accurate systematic observations of the moon and the planets and their positions with respect of the fixed stars. 600 BCE saw the development of mathematical astronomy with evidence of the influence Babylonian astronomy in Greek astronomy.

In conclusion it is with credit for the ancient Babylonian astronomy diaries that more complex and refined mathematical systems have been developed in later history. The influence of ancient Babylonian astronomy is clearly evident in Greek astronomy and mathematical number systems.

Ancient Babylonian astronomy is responsible for the development of the zodiac calendar from which later calendars have been developed in reflection of the study and frame works developed in Babylonian times.


Most interestingly ancient Babylonian astronomy gave us the seasons of the year, or more exactly they provided us with a system to predict the occurrence of seasonal changes.


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