How We Learned to Love the Invisible Sun

Eclipse edition special: looking back on 5,000 years of the human relationship with solar eclipses

I’m taking a short detour from the cosmic philosophy of my previous column to share a few thoughts about solar eclipses and the history of science. The immediate inspiration comes from the April 8, 2024 eclipse that cuts straight across North America, natch, but eclipses are an inspiring, recurring natural event all across the world. Heck, if you’re willing to wait, another great North American eclipse will slide by in 2045.

My real interest here is in the historical significance of eclipses as an indication of intellectual progress. The human eye worked exactly the same in ancient times as it does today. The capacity of the human mind was presumably exactly the same back then, as well. The way that we perceive eclipses is totally different, however, as is the meaning that we take from them.

Go back 5,000 years, and a solar eclipse was an inexplicable, portentous event. The Sun, the source of light and life, briefly vanished and was replaced by bizarre, glowing crown. We have only fragmentary awareness of what exactly ancient peoples thought about eclipses, but from what we know eclipses were commonly regarded as moments of great astrological significance, and perhaps of divine discontent.

It took thousands of years to be able to predict roughly when solar eclipses would happen, stripping away the sense that they happened at the whimsy of the gods. Then it took centuries more, along with an understanding of celestial mechanics and the laws of gravity, to reframe eclipses as a benign outcome of a clockwork universe.

Today, we have telescopes that can produce artificial solar eclipses on demand. We have spacecraft that observe solar eclipses from vantages beyond Earth, and soon we’ll have one that can create ones, too. We have two probes (NASA’s Parker Solar Probe and ESA’s Solar Orbiter) exploring the Sun up close, dipping directly the corona that we see as that crown around the eclipsed Sun.

For most people today, the “meaning” of a solar eclipse is that it’s a moment of natural beauty – a time when people who don’t normally pay much attention to the sky get a reminder that, yes, the Moon is a big rock that can occasionally pass in front of the Sun. The only folks who regard eclipses with fear these days are the ones who enjoy a little scare — the same psychological desire that compels people to watch horror movies, perhaps.

From a scientific perspective, solar eclipses are interesting but no longer terribly significant. What’s most notable about them is that they show how far we have come as a species. An elementary-school-level lesson about what the Sun is, and about how it shines, contains a level of awareness that was unavailable to the most educated scholars of just a couple centuries ago.

Solar eclipses remain just as rare and spectacular as they always have been. Now we can look at them without fear or bafflement, though. Over thousands of years, their beauty has grown deeper: not because our eyes have changed, but because of the rich cultural knowledge we all carry with us in the brains behind them.

Great Moments in Early Eclipse History

Let’s not get too smug, though. When you read popular accounts of the ancient mythology of eclipses, take them with a grain of salt. A lot of the reports have a suspicious tone of ahistorical condescension to them: “Weren’t those old-timey people so dumb and superstitious compared to us?”

Take, for instance, an oft-repeated tale that ancient Chinese emperor Chung K’ang beheaded two of his court astronomers, Hsi and Ho, for failing to predict a terrifying solar eclipse. Cool story, bro, but it’s probably a legend or a mistranslation.  

Here are some moments in solar eclipse history that really do stick out: Times when people stretched and elevated our collective comprehension of the celestial world.

• 5000 years ago: Concentric circles engraved in a stone tomb, now known as the Loughcrew Megalithic Monument in Ireland, might represent a solar eclipse that occurred there on November 30, 3340 BCE. Or maybe not; the pattern is not definitive, and the dating of the eclipse is only approximate. At the very least, this is an early example of an abstract artistic motif that very likely takes its inspiration from patterns in nature.

• c. 2000 BCE: The Chinese text Shujing records a startling event when “the Sun and Moon did not meet harmoniously.” This could refer to a solar eclipse from 2137 BCE, which would make it the earliest known written account of an eclipse.

• March 5, 1222 BCE: One of the earliest well-established observation a solar eclipse was recorded inscribed in a clay tablet from Ugarit, a city in what is now Syria. Researchers have connected that tablet to the eclipse of 1222 BCE, which helps establish the historical chronology of that era.

• May 28, 585 BCE: The Greek historian Heroditus claims that Thales of Miletus made history’s first successful solar eclipse prediction, forecasting an eclipse that inspired the end of conflict between the warring Lydians and the Medes. Take this one with a grain of salt, too, but it does seem likely that Thales recognized enough of a pattern to figure out when an eclipse was likely. But it was a one-shot deal; he didn’t know enough to ever predict another.

  

• c. 1230 CE: Were the Middle Ages a time of ignorance and darkness? The astronomical writings of Johannes de Sacrobosco (aka John of Hollywood) handily refute that myth. Even within a Sun-centered cosmology, he provided detailed and accurate illustrations of how a solar eclipse works, including the geometry of the Moon’s shadow sweeping across the Earth.

• 1519: Art and science mingle together elegantly in Isaac and Rebecca Spied upon by Abimelech, a painting by the renowned Renaissance artist Raphael (or, more likely, by members of his workshop). The painting shows an eclipsed Sun and includes a lushly detailed depiction of streamers in the solar corona.

Modern Science Meets the Sun

• June 1, 1639: Polish astronomer Johannes Hevelius produced an extraordinary series of precise observations of the Sun as it is covered and uncovered by the Moon. Shown in rapid sequence, they could be regarded as the first animation of a solar eclipse. I encourage you to visit the link to see for yourself.

• May 3, 1715: Back in days of ancient Greece, Thales had to fake it. Edmund Halley (yes, the one of comet fame) was able to predict a solar eclipse for real, with a timing accuracy of just 4 minutes! That’s what you can do when you understand the elliptical motions of celestial objects and have access to Newton’s equations of gravity. Or, as Jesse Pinkman might say, “yeah science, bitches!”

• July 8, 1842: The earliest notable scientific expedition devoted to the study of a solar eclipse. It helped that the eclipse path crossed Italy and France, so European researchers didn’t have to travel far. This expedition yielded the first clear descriptions of solar prominences, plasma eruptions on the Sun.

• July 28, 1851: The first photograph of a solar eclipse. Strictly speaking it was a daguerreotype, taken by Johann Julius Friedrich Berkowski working under the direction of August Busch, head of the Königsberg observatory in Prussia. Berkowski did a bang-up job. A solar eclipse is not an easy thing to photograph even today.

• October 20, 1868: The first artificial eclipse. Norman Lockyer, one of the most notable astronomers of the 19^th century, created an ingenious device that siphoned away most of the light of the solar disk while leaving the Sun’s outer layers visible. In this way, Lockyer discovered the chromosphere, a hot layer just above the visible surface of the Sun. He also discovered helium on the Sun: the first element ever discovered in space before it was known on Earth.

• May 29, 1919: The most consequential eclipse in modern times. Albert Einstein published the final version of this general theory of relativity in 1916, providing a revolutionary view of gravity, space, and time. His theory predicted exactly how starlight should be bent by the gravitational pull of the Sun, something visible only during a solar eclipse. Two expeditions in 1919 verified Einstein’s prediction, validated general relativity, and transformed Einstein into an international science celebrity. (Fateful twist: Einstein’s earlier version of general relativity contained an error that predicted the wrong amount of bending; if the eclipse test had been done earlier, it would have appeared to contradict relativity!)

The Future of Eclipses

By a lovely coincidence, the Moon and Sun appear almost the exact same size in Earth’s sky. (The Sun is 400 times wider than the Moon, but also 400 times farther away.) When the Moon is in the outer part of its orbit, it appears slightly smaller than the Sun, creating an annular eclipse that leaves a full ring of sunlight. When the Moon is at the inner part of its orbit, we get the full, glorious solar-eclipse experience. At least, that’s how things work today.

Due to the gravitational interaction between Moon and Earth, the Moon is gradually drifting away from us. About 650 million years from now, it will have spiraled far enough away that the Moon will never be able to completely cover the Sun. Even at its closest point, all the solar eclipses will be drowned out by a ring of light. From that moment on, there will never again be a total solar eclipse on Earth.

Take it as another kind of history lesson. Nothing is forever in our ever-changing universe, not even solar eclipses. Enjoy the special things while they last.