In the spring of 585 B.C. in the Eastern Mediterranean, the moon came out of nowhere to hide the face of the sun, turning day into night.
Back then, solar eclipses were cloaked in scary uncertainty. But a Greek philosopher was said to have predicted the sun’s disappearance. His name was Thales. He lived on the Anatolian coast — now in Turkey but then a cradle of early Greek civilization — and was said to have acquired his unusual power by abandoning the gods.
The eclipse had an immediate worldly impact. The kingdoms of the Medes and Lydian had waged a brutal war for years. But the eclipse was interpreted as a very bad omen, and the armies quickly laid down their arms. The terms of peace included the marriage of the daughter of the king of Lydia to the son of the Median king.
The impiety of Thales had a more enduring impact, his reputation soaring over the ages. Herodotus told of his foretelling. Aristotle called Thales the first person to fathom nature. The classical age of Greece honored him as the foremost of its seven wise men.
Today, the tale illustrates the awe of the ancients at the sun’s disappearance and their great surprise that a philosopher knew it beforehand.
The episode also marks a turning point. For ages, eclipses of the sun were feared as portents of calamity. Kings trembled. Then, roughly 2,600 years ago, Thales led a philosophical charge that replaced superstition with rational eclipse prediction.
Today astronomers can determine — to the second — when the sun on April 8 will disappear across North America. Weather permitting, it’s expected to be the most-viewed astronomical event in American history, astonishing millions of sky watchers.
“Everywhere you look, from modern times back, everyone wanted predictions” of what the heavens would hold, said Mathieu Ossendrijver, an Assyriologist at the Free University of Berlin. He said Babylonian kings “were scared to death by eclipses.” In response, the rulers scanned the sky in efforts to anticipate bad omens, placate the gods and “strengthen their legitimacy.”
By all accounts, Thales initiated the rationalist view. He’s often considered the world’s first scientist — the founder of a radical new way of thinking.
Patricia F. O’Grady, in her 2002 book on the Greek philosopher, called Thales “brilliant, veracious, and courageously speculative.” She described his great accomplishment as seeing that the fraught world of human experience results not from the whims of the gods but “nature itself,” initiating civilization’s hunt for its secrets.
Long before Thales, the ancient landscape bore hints of successful eclipse prediction. Modern experts say that Stonehenge — one of the world’s most famous prehistoric sites, its construction begun some 5,000 years ago — may have been able to warn of lunar and solar eclipses.
While the ancient Chinese and Mayans noted the dates of eclipses, few early cultures learned how to predict the disappearances.
The first clear evidence of success comes from Babylonia — an empire of ancient Mesopotamia in which court astronomers made nightly observations of the moon and planets, typically in relation to gods and magic, astrology and number mysticism.
Starting around 750 B.C., Babylonian clay tablets bear eclipse reports. From ages of eclipse tallies, the Babylonians were able to discern patterns of heavenly cycles and eclipse seasons. Court officials could then warn of godly displeasure and try to avoid the punishments, such as a king’s fall.
The most extreme measure was to employ a scapegoat. The substitute king performed all the usual rites and duties — including those of marriage. The substitute king and queen were then killed as a sacrifice to the gods, the true king having been hidden until the danger passed.
Initially, the Babylonians focused on recording and predicting eclipses of the moon, not the sun. The different sizes of eclipse shadows let them observe a greater number of lunar disappearances.
The Earth’s shadow is so large that, during a lunar eclipse, it blocks sunlight from an immense region of outer space, making the moon’s disappearance and reappearance visible to everyone on the planet’s night side. The size difference is reversed in a solar eclipse. The moon’s relatively small shadow makes observation of the totality — the sun’s complete vanishing — quite limited in geographic scope. In April, the totality path over North America will vary in width between 108 and 122 miles.
Ages ago, the same geometry ruled. So the Babylonians, by reason of opportunity, focused on the moon. Eventually, they noticed that lunar eclipses tend to repeat themselves every 6,585 days — or roughly every 18 years. That led to breakthroughs in foreseeing lunar eclipse probabilities despite their knowing little of the cosmic realities behind the disappearances.
“They could predict them very well,” said John M. Steele, a historian of ancient sciences at Brown University and a contributor to a recent book, “Eclipse and Revelation.”
This was the world into which Thales was born. He grew up in Miletus, a Greek city on Anatolia’s west coast. It was a sea power. The city’s fleets established wide trade routes and a large number of colonies that paid tribute, making Miletus wealthy and a star of early Greek civilization before Athens rose to prominence.
Thales was said to have come from one of the distinguished families of Miletus, to have traveled to Egypt and possibly Babylonia, and to have studied the stars. Plato told how Thales had once tumbled down a well while examining the night sky. A maidservant, he reported, teased the thinker for being so eager to know the heavens that he ignored what lay at his feet.
It was Herodotus who, in “The Histories,” told of Thales’s predicting the solar eclipse that ended the war. He said the ancient philosopher had anticipated the date of the sun’s disappearance to “within the year” of the actual event — a far cry from today’s precision.
Modern experts, starting in 1864, nonetheless cast doubt on the ancient claim. Many saw it as apocryphal. In 1957, Otto Neugebauer, a historian of science, called it “very doubtful.”
In recent years, the claim has received new support. The updates rest on knowledge of the kind of observational cycles that Babylon pioneered. The patterns are seen as letting Thales make solar predictions that — if not a sure thing — could nevertheless succeed from time to time.
If Stonehenge might do it occasionally, why not Thales?
Mark Littmann, an astronomer, and Fred Espenak, a retired NASA astrophysicist who specializes in eclipses, argue in their book, “Totality,” that the date of the war eclipse was relatively easy to predict, but not its exact location. As a result, they write, Thales “could have warned of the possibility of a solar eclipse.”
Leo Dubal, a retired Swiss physicist who studies artifacts from the ancient past and recently wrote about Thales, agreed. The Greek philosopher could have known the date with great certainty while being unsure about the places where the eclipse might be visible, such as at the war’s front lines.
In an interview and a recent essay, Dr. Dubal argued that generations of historians have confused the philosopher’s informed hunch with the precision of a modern prediction. He said Thales had gotten it exactly right — just as the ancient Greeks declared.
“He was lucky,” Dr. Dubal said, calling such happenstance a regular part of the discovery process in scientific investigation.
Over the ages, Greek astronomers learned more about the Babylonian cycles and used that knowledge as a basis for advancing their own work. What was marginal in the days of Thales became more reliable — including foreknowledge of solar eclipses.
The Antikythera mechanism, a stunningly complex mechanical device, is a testament to the Greek progress. It was made four centuries after Thales, in the second century B.C., and was found off a Greek isle in 1900. Its dozens of gears and dials let it predict many cosmic events, including solar eclipse dates — though not, as usual, their narrow totality paths.
For ages, even into the Renaissance, astronomers kept upgrading their eclipse predictions based on what the Babylonians had pioneered. The 18-year cycle, Dr. Steele of Brown University said, “had a really long history because it worked.”
Then came a revolution. In 1543, Nicolaus Copernicus put the sun — not Earth — at the center of planetary motions. His breakthrough in cosmic geometry led to detailed studies of eclipse mechanics.
The superstar was Isaac Newton — the towering genius who in 1687 unlocked the universe with his law of gravitational attraction. His breakthrough made it possible to predict the exact paths of not only comets and planets but the sun, the moon and the Earth. As a result, eclipse forecasts soared in precision.
Newton’s good friend, Edmond Halley, who lent his name to a bright comet, put the new powers on public display. In 1714, he published a map showing the predicted path of a solar eclipse across England in the next year.
Halley asked observers to determine the totality’s actual scope. Scholars call it history’s first wide study of a solar eclipse. In accuracy, his predictions outdid those of the Astronomer Royal, who advised Britain’s monarchy on astronomical matters.
Today’s specialists, using Newton’s laws and banks of powerful computers, can predict the movements of stars for millions of years in advance.
But closer to home, they have difficulty making eclipse predictions over such long periods of time. That’s because the Earth, the moon and the sun lie in relative proximity and thus exert comparatively strong gravitational tugs on one another that change subtly in strength over the eons, slightly altering planetary spins and positions.
Despite such complications, “it’s possible to predict eclipse dates more than 10,000 years into the future,” Dr. Espenak, the former NASA expert, said in an interview.
He created the space agency’s web pages that list solar eclipses to come — including some nearly four millenniums from now.
So, if you’re enthusiastic about the April 8 totality, you might consider what’s in store for whoever is living in what we today call Madagascar on Aug. 12, 5814. According to Dr. Espenak, that date will feature the phenomenon of day turning into night and back again into day — a spectacle of nature, not of malevolent gods.
Perhaps it’s worth a moment of contemplation because, if for no other reason, it represents yet another testament to the wisdom of Thales.