The oldest written records of eclipses are in cuneiform texts from around 2000 BC, but examination of oral traditions reveal First Nations astronomers were predicting eclipses by word of mouth
By Michael Marshall
19 March 2024
Florilegius/Universal Images/Getty
In 331 BC, the Macedonian warlord Alexander the Great marched his army into the territory of the Achaemenid Empire and its king Darius III. Alexander went into the battle highly confident, partly because he believed there had been a good omen: a near-total lunar eclipse a few days before, on the night of 20-21 September. The Battle of Gaugamela, in what is now Iraqi Kurdistan, ended in a decisive victory for Alexander. Darius fled for his life, and Alexander soon took over the entire Achaemenid Empire. That’s one powerful lunar eclipse.
From our perspective, it is easy to look at such stories and dismiss ancient peoples’ ideas about phenomena like eclipses as ignorant and superstitious. But careful examination of ancient texts and oral traditions reveals that people understood something of the mechanics of the solar system and even had some ability to predict eclipses.
Mesopotamian astronomy
The oldest known written records of astronomical phenomena, including eclipses, come from Mesopotamia, according to Clemency Montelle at the University of Canterbury in New Zealand in her 2011 book Chasing Shadows.
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Montelle describes a set of several dozen cuneiform tablets known as the Enūma Anu Enlil, 13 of which contain information about lunar and solar eclipses, compiled between 2000 and 1600 BC. The main purpose of the tablets seems to have been to alert the king about omens. In the process, the astronomers began to see patterns. For example, they recognised that lunar eclipses only occur during a full moon and solar eclipses during a new moon. Later, Assyrian astronomers may have noticed that lunar eclipses tend to recur either every six months or after a longer interval.
These early astronomers faced two major challenges in predicting eclipses. The first was that eclipses do recur in predictable ways, but only over very long timescales. Near-identical eclipses occur every 6585.3 days, or just over 18 years: a period called the saros. To spot this 18-year saros cycle, you need decades of observations, and a good calendar to boot.
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