How Eclipses Destroyed Empires, Enabled Columbus, and Inspired the Birth of Science

The umbral shadow of the moon. Credit Rob Glover.

Tonight at around 7:50pm EST, the Earth's outer shadow will be cast upon the moon, causing a penumbral eclipse. It will be visible in the early evening in the eastern Americas, while those in the Greenwich mean time zone will be be treated to a perfect midnight showing. Eastern Europeans and Asians will have to compete with the sunrise to get a glimpse of the eclipse in the early morning of October 19.

Though penumbral eclipses aren't as dramatic as total lunar eclipses, the subtle shading of the moon's southeastern chunk is still an exciting event for stargazers. Even a modest eclipse is worth checking out, if only because these orbital shadow puppet shows have such a profound effect on the development of our weird species. Lunar eclipses have hastened the fall of juggernaut empires, sparked the scientific method, and inspired some aggressively insane myths.

Indeed, eclipses were the blockbusters of the ancient world: everybody had an opinion on whether they were good or bad, and what had inspired them. Solar eclipses, with their unnerving ability to blot out the sun, were probably more feared than the lunar variety. But as astroarcheologist Clive Ruggles points out, ancient civilizations didn't take either lightly.

“For modern city dwellers, it is easy to miss even a total lunar eclipse, and for this reason we are inclined to think that for ancient peoples the social impact of a total solar eclipse—a truly rare event transforming day into night—would have been far greater,” he writes in Ancient Astronomy: An Encyclopedia of Cosmologies and Myth. “Yet anyone who relies upon the moon to illuminate a dark night or as the basis of their calendar regarding seasonal subsistence and ritual activities may be alarmed to watch the full moon being 'eaten' away and then totally consumed. […] To many peoples in the past, then, an eclipse of the moon was just ominous, potentially frightening, and even calamitous, as a total solar eclipse.”

The Aztec moon god Coyolxauhqui. Credit Miguel Alvarez Bernardo.

Indeed, pregnant Aztec women were afraid that the darkening of the moon would cause their children to be born without lips or noses, cross-eyed, or even as mice. The red tinge of the lunar surface during an eclipse—caused by light refracted in the prism of Earth's atmosphere—also inspired many cross-cultural stories about how the satellite was being violently bitten and swallowed. For example, the Egyptians believed that the god Seth, in pig form, engorged himself on the moon during eclipses, only to be forced by Thoth to barf it up again (Handbook of Egyptian Mythology, pg. 167). We now know the lunar surface is largely composed of regolith, but to the Egyptians, it was covered in a sheen of god-bile.

The demystification of lunar eclipses was kickstarted in ancient Sumer, where the advent of writing allowed for more detailed records of these ominous events.

“[The Sumerians] noticed a pattern in eclipses called the Saros cycle where eclipses tend to occur approximately every 18 years and 11 days,” NASA Goddard veteran and author Fred Espenak (better known by his well-earned nickname: Mr. Eclipse) told me. “After keeping historical records for hundreds of years of eclipses, they noticed the pattern and used that to extrapolate ahead into the future.”

But it's not as if the Sumerian predictions eclipsed, if you will, the superstitious belief that these events were portents of evil caused by petulant gods. “They just knew that this was a recurring pattern,” Espenak said. “What it was caused by, I don't think they had any idea.”

Indeed, astrolatry—the worship of celestial bodies as deities—was a widespread practice, and there were cross-cultural permutations of eclipse predictions across many Bronze Age civilizations. The Shang dynasty of the second millennium BCE, for example, regarded the prediction of lunar eclipses as a completely divinatory practice with little real-world application. The Maya, meanwhile, were so obsessed with squaring the natural cycles of eclipses with their own manmade mythologies that they plotted out appropriate rituals on all 260 days of their calendar.

“In complete contrast to the ancient Chinese,” Ruggles said, “the desire to incorporate what were effectively astrological considerations into their calendar drove the Maya to ever greater levels of astronomical achievement.” In other words, the false premise that crazy sky-beings were behind lunar eclipses often spurred scientific advances, rather than dissuading them.

However, the mutually beneficial relationship of astrolatry and astronomy began to fray somewhat in the tumultuous world of 5th and 4th Century BCE Greece. These centuries saw the birth of philosophy, including early stabs at the scientific method, alongside a superstitious brinkmanship culture that culminated in the Peloponnesian War. Lunar eclipses were central to both the birth of science during this time, and the demise of the Greek golden age as a result of the region's unchecked military campaigns.

The scientific front was kicked off by Anaxagoras of Clazomenae (c. 510-428 BCE), who blazed into Athens around the middle of the 5th Century, spouting off Ionian philosophy at whoever would listen. He was one of the first philosophers who refused to explain natural phenomena in mythological terms, and this skeptical perspective helped him figure out the real mechanics behind eclipses. He understood that the moon shone by reflected light, and that both solar and lunar eclipses were caused by the position of the Earth, moon, and sun relative to each other.

Anaxagoras with his own shadow on a globe. Credit Eduard Lebiedzki.

Naturally, Anaxagoras was kicked out of Athens on charges of heresy. But you can't exile ideas, and many philosophers took up the scientific mantle after him. For example, Aristotle used lunar eclipses to prove the Earth was round.

“He noticed after looking at eclipses at different times of the night and different parts of the sky that the shape of that shadow was always curved,” said Espenak. “The only thing that always produces a curved shadow is a sphere.” Not only had lunar eclipses helped contextualize the position of the Earth relative to the moon and the sun, they had given our planet a shape.

Lunar eclipses also exercised huge influence over the outcome of the Peloponnesian War. From 415-412 BCE, Athens was embroiled in one of the most catastrophic military fuck-ups in history: the Sicilian Expedition. The Athenians learned the age-old lesson “never go in against a Sicilian when death is on the line” the hard way in this campaign. They tried to take the island quickly but were round-house kicked by the impressive native cavalry and the Syracusan/Spartan alliance.

Exhausted and demoralized, the lead general Nicias finally agreed to sail back to Athens with what was left of the army in the summer of 412. But on the night of August 27-28, just as they were preparing to leave, a total lunar eclipse took place. Nicias' spiritual advisors told him it would be wise to wait for 27 days before escaping, which is a real contender for the Worst Advice Ever Olympics.

Unfortunately, Nicias was a deeply superstitious man. He accepted the counsel of his priests, and thus wrote his own death sentence. The Syracusans took the opportunity to block off any escape route, and the remainder of the Athenians were forced to flee into unfamiliar territory, until they were brutally slaughtered at the Assinarus river. The Sicilian victory was so decisive that Athenians at home considered reports of it to be practical jokes for a long time. When more and more survivors returned from war, they finally recognized it for what it was: the last nail in the coffin of the Athenian golden age. Nicias and his generals were executed and the campaign was lost, all because of a lunar eclipse.

Even millennia after the Sicilian Expedition, when the scientific relevance of eclipses had faded, lunar brownouts still exercised incredible influence over history. For example, Christopher Columbus used a total lunar eclipse to dupe Jamaican natives into feeding his crew (which is so in character for him, it hurts). After six months of tolerating the beached Europeans shipwrecked on their shores, the indigenous population was sick of wasting their time and energy on their less-than-charitable guests, and cut off the food supply.

Columbus had an almanac covering astronomical events from 1475-1506 on board, and decided to use the upcoming total lunar eclipse on February 29, 1504 as a bargaining chip. He told the natives that god was pissed off about the food cutoff, and that he was going to show his anger by having the moon rise red with wrath on that date. The Jamaicans were so frightened when this actually took place that they immediately re-supplied the Europeans with provisions. They were relieved only when Columbus assured them that they were forgiven, after letting them marinate in dread for 48 hours. Thanks to the eclipse, Columbus was able to sustain his crew long until they were finally rescued on June 29, 1504.

Columbus hoodwinks the Jamaican natives. Credit: Camille Flammarion.

Though they are beautiful to behold, lunar eclipses obviously don't have the same sway – scientific or political – that they did a few hundred years ago. “Professional astronomers don't bother with lunar eclipses,” said Espenak. “There's really not much to be learned from them in this day and age. There are unusual exceptions but, by and large, astronomers don't pay any attention to them – professionally. Amateurs are a different story.”

Regardless of whether you are a professional or an amateur, this is an exciting decade for eclipse-lovers. In addition to the minor eclipse tonight, there will be a total lunar eclipse on April 15, 2014, which will be visible across North America. On top of that, a total solar eclipse will run through the center of the United States on August 21, 2017, an event which hasn't happened in almost 40 years.

Though a partial solar eclipse will be visible to all North Americans, Espenak recommends traveling to the narrow band that will behold the total solar eclipse.“It is only 100-150 miles wide, and it streaks across the country and produces what's called the path of totality,” said Espenak. “You've got to be in that narrow shadow path to actually see the total face of the eclipse. If you're outside that path, you'll see a partial eclipse, which is okay, but I like to compare it to the lottery. If you get 8 out of 9 numbers out of the lottery, you don't win. If you got 95% out of 100% of a partial eclipse, you don't win. It makes all the difference in the world.”

And he should know. The last time a solar eclipse's path of totality ran through the continental US was on February 26, 1979, and it was responsible for inspiring Espenak to become Mr. Eclipse. “I had to drive 600 miles to get to it,” he said. “I was just a kid, but I had been planning on it for like, six or seven years.” It was worth the years of preparation. “A total eclipse is one of the most spectacular things you can possibly see.”

For those interested in following Espenak's example, the path of totality for 2017 eclipse is mapped out below. There will be two other opportunities to see total solar eclipses before 2017, though the paths of totality for those events will mostly fall across the ocean. Even so, on March 20, 2015 a total eclipse will be visible from the remote Faroe Islands, and a few lucky Caribbean islands will be in the path of the March 9, 2016 eclipse.

The path of totality across the continental United States on August 21, 2017. Credit: Fred Espenak.

So update your calendar, and enjoy the penumbral eclipse tonight. Though it won't be as spectacular as a total blackout, it will possess the same eerie magnetism that has inspired some of our greatest achievements and most frenzied panic attacks over the centuries. And, just for old time's sake, imagine that the moon is being devoured alive by some ravenous god-beast. Our ancestors would appreciate it, before advising us to do incredibly dumb stuff because the moon said so.