First Nations astronomers predicted eclipses without using writing

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.

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.

Secondly, eclipses are never visible from the whole of Earth’s surface. The eclipse that comes 18 years after the last one might only be visible from the other side of Earth. Confined to one corner of the planet, the Mesopotamians only knew about the eclipses that were seen from their area – giving them an incomplete picture.

These difficulties were less pronounced for lunar eclipses, which can be seen from Earth’s entire night side and often last over an hour. In contrast, solar eclipses are only visible along a narrow band of Earth’s surface and last mere minutes. Lunar eclipses are inherently more predictable, which is why Mesopotamian astronomers were already spotting patterns in them.

Mayan eclipse records

Similar stories played out on the other side of the planet, for instance in the Maya society of Mesoamerica. The Maya had an elaborate religion that included ideas about cosmology.

One of the most illuminating Mayan artefacts is a painted book called the Dresden Codex, named for the city in Germany where it is housed. It was probably created around AD 1210, perhaps in the Mayan city of Chichʼen Itzaʼ. In her 1999 book Star Gods of the Maya, Susan Milbrath at the University of Florida described a series of eclipse tables in the Dresden Codex. The tables seem to describe time intervals in which eclipses could occur, serving as predictions.

Recognising that the sun was essential for their survival, Mayan astronomers viewed eclipses as threatening. In some traditions, the end of the world would begin with an eclipse.

Nevertheless, there were limits. “The Dresden predictions are only accurate to the day, and they only indicate that the Maya calculated that somewhere on Earth there would be an eclipse on that date,” says Milbrath. Like the Mesopotamians, the Maya were unable to predict where on Earth eclipses would be visible.

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In subsequent centuries, astronomer-priests became good enough at predicting eclipses that they may have got sneaky about it.

In the early 1500s in the city-state of Tenochtitlan, in what is now Mexico, Mexica people (sometimes called Aztecs) carved a large circular stone. Now known as the Aztec calendar stone or sun stone, its densely packed symbols encode information about cyclical creation and destruction, including imagery of the sun and moon.

In a 2017 study, Milbrath argued that some of the imagery relates to a solar eclipse. She suggested the central image is the death of the sun god Tonatiuh during an eclipse, which was associated with the end of the world. In her view, the stone predicts a world-ending eclipse on a particular day of the year.

However, there was never an eclipse on this day during Aztec rule and there won’t be until 2078. Milbrath says this revelation, shown through calculations by Arnold Lebeuf, at the Jagiellonian University in Kraków, Poland, suggests astronomer-priests were trying to ensure their own long-term position by predicting a cataclysm they knew wouldn’t happen, but which they could use to scare the populace.

We know all of this because these cultures had writing. But what about societies that didn’t?

Eclipses in oral cultures

Understanding and predicting eclipses looks much harder if your society doesn’t have writing. Keeping track of when and where eclipses have happened would be tricky enough; spotting patterns and using them to predict future eclipses sounds like a tall order. Nevertheless, there is evidence that some non-literate societies pulled it off – at least for lunar eclipses.

Duane Hamacher at the University of Melbourne in Australia has spent years studying the astronomical knowledge of Aboriginal Australians. He summed up his findings in his 2022 book The First Astronomers, co-authored with Aboriginal and Torres Strait Islander Elders.

When Hamacher started, the popular belief was that Aboriginal Australians had “some stories and names for stuff”, but no “real astronomy”. “It didn’t take 10 seconds of looking into it to realise that’s total rubbish,” he says.

In a 2011 study, Hamacher and his colleague Ray Norris described several dozen Aboriginal accounts of eclipses. Like the Maya, they often viewed eclipses as threatening. But they also understood something of the mechanics.

For instance, the Pintupi people of the Central desert said a solar eclipse was caused by Pira (the moon man) covering the sun, either with his hand or body. “There were so many Aboriginal traditions that described this event as being when the moon covered up the sun,” says Hamacher. This is striking because the moon isn’t visible before a solar eclipse. “People know where celestial objects are even when you can’t see them.”

In a chapter of his book, written with Uncle Ghillar Michael Anderson of the Euahlayi Nation, Hamacher describes the Zugubau Mabaig (“astronomers”) of the western Torres Strait Islands. A key duty of a Zugubau Mabaig was to perform a ceremony called Melpal Mari Pathanu (“the ghost has taken the spirit of the moon”) during an eclipse. The Zugubau Mabaig recited the names of the Torres Strait Islands until the moon emerged.

Crucially, the ceremony was planned in advance, according to a man named David Bosun whose father was a Zugubau Mabaig. “Which means people had to predict when that lunar eclipse [was] going to occur,” says Hamacher.

We don’t know how the Zugubau Mabaig predicted the lunar eclipses: a lot of Aboriginal Australian astronomical knowledge was lost during European colonisation. However, Hamacher says one element that may have helped is how durable oral traditions can be.

In a study published in November 2023, he and his colleagues studied Tasmanian Aboriginal oral traditions. The traditions include a description of the flooding of the land bridge that once connected Tasmania to mainland Australia, about 12,000 years ago. They also refer to the star Canopus as being located near the southern celestial pole, which was the case about 14,000 years ago.

“Now that we’re understanding how oral tradition works a bit better, we know that huge bodies of knowledge can be committed to memory and they can last for thousands of years,” says Hamacher. This may help explain how societies without writing could nevertheless predict phenomena as intermittent as eclipses.

Predicting eclipses may seem like an esoteric skill for hunter-gatherer societies, but Hamacher says we shouldn’t be surprised. “The sky is how you measure time,” he says. “I mean really, how do you measure time without the sun, moon or stars?” Studying it offered ways to keep track of crucial cycles like tides and animal migrations. “Astronomy is always something that ancient cultures would have figured out how it works, because it would be necessary to thrive and survive.”