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Tuesday, August 15, 2017

Was the First Eclipse Prediction an Act of Genius, a Brilliant Mistake, or Dumb Luck? | Atlas Obscura - Eclipse Madness

Photo: Natasha Frost
It is hard to predict an eclipse when you think the world is flat, notes Natasha Frost, British-Kiwi hybrid and Atlas Obscura Editorial Fellow.

Thales, in an 18th-century engraving by F. Ramberg.  
Photo: Wellcome Images/Public Domain


The year was 585 B.C., and the Lydians and the Medes had been warring for half a decade in what we now know as Turkey. No clear victory was in sight. Sometimes the Lydians were on top, on other occasions, the Medes seemed to have matters in hand. Once they even fought a battle in the dead of night. But, in the sixth year of their war, as they brandished their arms on the battlefield, something amazing happened. The skies began to darken. The moon passed in front of the sun. The armies, astonished, lay down their weapons—and called a truce.

This story comes to us via Herodotus, the Greek historian, who lived about a century after the fight. What’s perhaps more remarkable about this story is the line that follows it: “Thales of Miletus had foretold this loss of daylight to the Ionians, fixing it within the year in which the change did indeed happen.”

The ancient philosopher Thales of Miletus had no access to the scientific knowledge or equipment to successfully predict a solar eclipse. As a result, this story has puzzled and divided classicists and scientists for centuries. Was it preternaturally sophisticated astronomy, a myth, or just a happy accident?

Researchers believe that the eclipse Herodotus describes over the battlefield is the one that took place on May 28, 585 B.C. Its path ran from Nicaragua, over the Atlantic, then across France and Italy—and, finally, Turkey. Thales’s home, the ancient city of Miletus, on the Mediterranean coast, is just outside the path of totality. He would have seen an impressive partial eclipse from there. There are other eclipses around that time that are possible candidates, but none that would have plunged the Lydians and Medes into abrupt darkness in the way that Herodotus describes.

It is particularly strange, if the historian is to be taken at his word, that Thales predicted the year of the eclipse, rather than the exact date. In fact, wrote mathematician Dmitri Pachenko in the Journal for the History of Astronomy, “if one can predict an eclipse at all, one can predict it to the day.” Astronomy is an extremely precise science. If you know a major celestial event is coming, and where it will be visible, you’ll most likely have some precision about when it will take place. Thales, however, was at a marked disadvantage for making astronomical predictions. He didn’t know that the Earth is spherical—and seems to have thought of it as a flat disc, resting on water. 

So how did he do it? A common suggestion is that Thales had coopted the expertise of the ancient Babylonians. Their astronomers, based near modern Baghdad, kept careful records of the sky, including how Venus, Mercury, the Sun, and the Moon moved in the heavens. In 1063 B.C., their records document a total eclipse “that turned day into night.” These records led them to discover what we now call the Saros cycle, which governs the recurrence of eclipses. After three 223-month Saros series, eclipses do return to the same geographic region, but they are a complicated way to make an eclipse prediction. At any given moment, there are approximately 40 Saros cycles taking place at once, carrying on for over 1,000 years. As old sets of cycles end, new ones begin. Understanding them enough to be predictive, at the very least, requires the knowledge that the Earth is round and accurate, detailed observations—not to mention accounting for those missed eclipses that take place on cloudy days.

Thales did feats of mathematics that might have looked like magic to his contemporaries, including calculating the height of the pyramids from the length of their shadows. He was a legend. It’s possible, then, that his famous prediction was, too. People so readily accepted his claims—that magnets have souls because they make things move, that earthquakes happen because the Earth is floating on water, that all things are full of gods—that it wasn’t much of a stretch to believe he could have predicted mysterious happenings in the sky.

Natasha Frost ends his article with the following: Thales did feats of mathematics that might have looked like magic to his contemporaries, including calculating the height of the pyramids from the length of their shadows. He was a legend. It’s possible, then, that his famous prediction was, too. People so readily accepted his claims—that magnets have souls because they make things move, that earthquakes happen because the Earth is floating on water, that all things are full of gods—that it wasn’t much of a stretch to believe he could have predicted mysterious happenings in the sky.

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The so-called Venus Tablet of Ammisaduqa, from ancient Mesopotamia, shows detailed astrological forecasts.
Photo: Fae/CC BY 3.0
 "Some methods are easier than others." 

Source: Atlas Obscura


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