Planetary theory

Babylonian planetary theory emerged not from curiosity but from administrative necessity and religious obligation. Temple astronomers—the tupšar Enûma Anu Enlil—served dual roles: interpreting celestial omens for kings and managing economic timetables for tax collection. The same priest tracking Jupiter's position oversaw agricultural schedules tied to seasonal flooding of the Euphrates.

The Venus Tablet of Ammisaduqa, compiled during the reign of Babylon's tenth king after Hammurabi (circa 1646-1626 BCE), records 21 years of Venus observations. Scribes noted when the planet first appeared on the horizon before sunrise, when it disappeared into the sun's glare, and when it reappeared as an evening star. These weren't poetic musings—they were data points in an omen series, the Enūma Anu Enlil, where celestial events presaged earthly consequences for the kingdom.

What made Babylon's astronomy possible was infrastructure that no earlier civilization had assembled. Cuneiform writing on clay tablets created permanent records that survived burial. The sexagesimal (base-60) number system, inherited from Sumerians, made fraction calculations manageable—dividing by 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30 all yielded clean integers. Temple observatories maintained continuous records across centuries, and scribal schools (edubbas) transmitted computational techniques through hereditary lineages.

By 750 BCE, Babylonian astronomers began systematic daily observations that continued for over 600 years. These Astronomical Diaries recorded planetary positions, lunar and solar eclipses, weather patterns, commodity prices, and river levels—an empirical database unprecedented in human history. From this accumulation, patterns emerged. Jupiter returned to the same position against the stars every 12 years. Venus completed its cycle in roughly 8 years. Eclipse sequences repeated every 18 years (the Saros cycle).

The MUL.APIN tablets, compiled around 1000 BCE but containing observations dating to 1200 BCE or earlier, organized this knowledge systematically. Sixty-six stars and constellations were grouped into three celestial paths: the path of Enlil (northern), Anu (equatorial), and Ea (southern). Planetary visibility periods were catalogued: Venus visible for roughly 5 months as evening star, invisible for 7 months, visible for 5 months as morning star, invisible for 3 months.

The breakthrough came in the last centuries BCE when Babylonian mathematicians developed geometric methods to calculate Jupiter's displacement—computing the area under a velocity-time curve to predict position. This proto-calculus predated European calculus by 1,400 years. Four procedure texts from 350-50 BCE show the technique clearly.

China developed planetary astronomy independently from the late fourth millennium BCE, organizing different constellations (28 lunar mansions versus Babylon's zodiacal approach) and emphasizing polar stars over the ecliptic. Scholar Asko Parpola confirmed in 2013 that hypotheses of Mesopotamian diffusion to China and India were unfounded—these were parallel evolutionary paths, convergent solutions to the same problem of predicting celestial motion.

The Babylonian tradition cascaded directly into Greek astronomy. Around 280 BCE, the priest Berossus moved from Babylon to the Greek island of Kos to teach Babylonian methods. Hipparchus accessed Babylonian records directly, adopting their numerical parameters for planetary periods. Every subsequent variety of scientific astronomy—Hellenistic, Indian, Islamic, European—depends on Babylonian astronomy in fundamental ways.