# Talk abstract details

Planetary data and predictions in Babylonian Goal-Year Astronomy

### Abstract

Mesopotamian astronomers during the Late Babylonian Period (c. 750 BC to AD 75) made nightly observations of planetary and lunar phenomena. Drawn from these initial observations, several mathematical schemes were developed for predicting astronomical events, whilst at the same time empirical methods were developed for predicting the same events. Hence a large body of astronomical material remains from this period covering observations, calculations and predictions of astronomical events. This material is generally divided into two categories: mathematical texts, which include theoretical schemes and calculated predictions; and non-mathematical texts, which include observations and empirical predictions derived from these observations.

This study focuses particularly on the empirical methods which the Babylonian astronomers developed to predict certain astronomical phenomena. The process involved predicting future occurrences of the same astronomical events by identifying periods, known as Goal-Year periods, over which the events occur on roughly the same date in the Babylonian calendar. The events which were predicted in this way concerned either the moon or one of the five planets known to the Babylonian astronomers: Mercury, Venus, Mars, Jupiter and Saturn.

Goal-Year periods were then used to compile the Babylonian non-mathematical texts known as Goal-Year Texts – texts composed of excerpts from various Diaries. The records for events relating to each planet come from the Diary for a particular year, using the periodic motion of the moon and planets to create rough predictions for the events of the “goal year”:

Mercury 46 years

Venus 8 years

Mars 47 and 79 years

Jupiter 83 and 71 years

Saturn 59 years

Moon 18 and 19 years

So a Goal-Year Text for any particular Babylonian year therefore contains Mercury observations from the Diary 46 years earlier, Venus observations from the Diary 8 years earlier, and so on to create rough predictions of what planetary and lunar events to expect during the “goal year” (Sachs 1948, Hunger 1999).

This talk will use examples of planetary data from the various non-mathematical observational and predictive texts to study some of the relationships between astronomical texts of the Late Babylonian period. In particular I study the use of Goal-Year Texts in compiling the predictive texts known as Almanacs and Normal Star Almanacs. In addition to this, records from procedure, observational and predictive texts will be used to give examples of which Goal-Year periods the Babylonian astronomers refer to in the various texts, including those referred to above, and demonstrate how some of them were used in practice.

The records used in this investigation have been taken from a variety of sources. The main sources used to obtain copies of texts were:

• Astronomical Diaries and Related Texts from Babylonia (Sachs & Hunger, 1988-2006), which provides translations of various non-mathematical texts.

• Late Babylonian Astronomical and Related Texts (Sachs, 1955), which contains hand-drawn copies of many astronomical cuneiform texts in the British Museum.

• Other previously published transliterations or translations of individual texts: Neugebauer & Sachs (1967), Sachs (1976), Sachs & Walker (1984), Roughton (2002).

• Translations of texts not previously published obtained by personal study of the texts at the British Museum.

The present investigation considers planetary data only; similar analyses of lunar data have been undertaken by Brack-Bernsen (1999).

This study focuses particularly on the empirical methods which the Babylonian astronomers developed to predict certain astronomical phenomena. The process involved predicting future occurrences of the same astronomical events by identifying periods, known as Goal-Year periods, over which the events occur on roughly the same date in the Babylonian calendar. The events which were predicted in this way concerned either the moon or one of the five planets known to the Babylonian astronomers: Mercury, Venus, Mars, Jupiter and Saturn.

Goal-Year periods were then used to compile the Babylonian non-mathematical texts known as Goal-Year Texts – texts composed of excerpts from various Diaries. The records for events relating to each planet come from the Diary for a particular year, using the periodic motion of the moon and planets to create rough predictions for the events of the “goal year”:

Mercury 46 years

Venus 8 years

Mars 47 and 79 years

Jupiter 83 and 71 years

Saturn 59 years

Moon 18 and 19 years

So a Goal-Year Text for any particular Babylonian year therefore contains Mercury observations from the Diary 46 years earlier, Venus observations from the Diary 8 years earlier, and so on to create rough predictions of what planetary and lunar events to expect during the “goal year” (Sachs 1948, Hunger 1999).

This talk will use examples of planetary data from the various non-mathematical observational and predictive texts to study some of the relationships between astronomical texts of the Late Babylonian period. In particular I study the use of Goal-Year Texts in compiling the predictive texts known as Almanacs and Normal Star Almanacs. In addition to this, records from procedure, observational and predictive texts will be used to give examples of which Goal-Year periods the Babylonian astronomers refer to in the various texts, including those referred to above, and demonstrate how some of them were used in practice.

The records used in this investigation have been taken from a variety of sources. The main sources used to obtain copies of texts were:

• Astronomical Diaries and Related Texts from Babylonia (Sachs & Hunger, 1988-2006), which provides translations of various non-mathematical texts.

• Late Babylonian Astronomical and Related Texts (Sachs, 1955), which contains hand-drawn copies of many astronomical cuneiform texts in the British Museum.

• Other previously published transliterations or translations of individual texts: Neugebauer & Sachs (1967), Sachs (1976), Sachs & Walker (1984), Roughton (2002).

• Translations of texts not previously published obtained by personal study of the texts at the British Museum.

The present investigation considers planetary data only; similar analyses of lunar data have been undertaken by Brack-Bernsen (1999).