Transit of wonder

Listen to this essay 21 minute listen There is something comical about the fact that the planet named for the goddess of love once drove the scientific world to its knees. During a transit, Venus passes between Earth and the Sun, becoming a small black dot against the solar disk. These events are among astronomy’s rarest spectacles. They come in pairs eight years apart, then disappear for more than a century. The last one was in 2012, when Venus crossed the face of the Sun as a small black dot, its journey livestreamed around the world. Scientists and enthusiasts watched something they would never see again in their lifetimes – from terraces with eclipse glasses or on their laptops from the comfort of their homes. But a quarter of a millennium ago, scientists didn’t have that luxury. Astronomers risked everything to see this small shadow in the name of science. The quest was romantic in the classic sense: obsessive, impractical and grand. As with the era’s poetry and painting, its romance was inseparable from the empire that produced it. It all started when I walked into a tiny museum at Harvard University. I’m a science writer, which is what happens when you love physics but physics doesn’t quite love you back. I have a master’s degree in it, but the intuition for research never really hit me right. Still, I couldn’t shake the feeling that there was something I could give science. Most people don’t see science the way I do – as something interesting, beautiful, even emotional. So, naturally, I did what no tortured artist has ever done before: I started writing about my unrequited love. I wanted people to see the science that I see, and feel it the way I do. If I got lucky, I’d find one of those stories that make science feel human. Stories of people who cared too much. The ones who spent years chasing starlight or boiling mercury, convinced that, if they just measured carefully enough, everything would finally make sense. They believed the Universe could be solved with mathematics and patience. I couldn’t tell if I was drawn to those old stories because they were profound or just nostalgic – and the Putnam Gallery in Cambridge, Massachusetts (less like a museum than a well-lit storage space) was where I would find out. The place was so little known that I was the only person there, aside from the woman at the front desk, and the quiet gave me the time to notice what became, to me, the funniest thing in the room: almost every instrument I looked at pointed to the same thing. A telescope built to track Venus. A map charting her path across the Sun. A pendulum clock precisely calibrated to catch the exact moment of her transit. Venus, Venus, Venus. The fact that so many astronomers seemed to be obsessed with Venus was ironic. Of all the astronomical bodies there were to observe, and all the other science there was to do, these old men were focused on the one planet named after the most beautiful woman in existence. Typical! Venus would appear to trace different paths across the Sun depending on where on Earth you were watching from Even though the joke was what pulled me in, I realised that the obsession had a purpose. It was about measuring the dimensions of the solar system. For centuries, astronomers knew the relative distances of the planets: Venus was closer to the Sun than Earth was, and Mars was further away. But they didn’t know the scale. They had the map but not the ruler. How many kilometres lay between Earth and the Sun? No one had a solid number. The key, it turned out, was the transit of Venus across the Sun. If astronomers timed the transit from far-out parts of the globe, they could use a phenomenon called parallax (the apparent shift of an object when you view it from two locations) to calculate the distance to the Sun. (Picture the tiny shift you see when you hold your thumb in front of your face and close one eye, then the other.) Scale up that effect to the size of the solar system, and Venus would appear to trace slightly different paths across the Sun depending on where on Earth you were watching from. Thus, with enough observations and enough mathematics, astronomers could triangulate Earth’s distance from the Sun. It was the English astronomer Edmond Halley who figured this out back in 1716. But he had a problem: as with all transits of Venus, opportunities came in pairs eight years apart, and then not again for more than a century. Halley knew he wouldn’t live to see the next one, so he left behind instructions urging future astronomers to observe the transits of 1761 and 1769. In 1761, even with wars raging across continents, astronomers took up Halley’s challenge. Backed by royal support and armed with the best instruments of the time, they set out for more than 70 observation sites around the globe. That was how all those telescopes, maps, clocks and quadrants had found their way, eventually, into this tiny museum: relics of a global campaign to measure a shadow. Though I was pulled in by the romance of it all, it wasn’t lost on me that the world these stories came from was far from romantic. For many of the astronomers, the expeditions might have been about discovery. But for the empires funding them, it was also about control: mapping trade routes, claiming territories and proving dominance. Captain James Cook, for instance, sailed to Tahiti to observe the transit of Venus in 1769, but his voyage also carried imperial instructions to chart and claim land for Britain. For Cook, measuring the heavens and expanding the empire were part of the same mission. Someone like me – a brown woman standing in a museum, tracing these stories with awe – wouldn’t have belonged in that world. The imperialism, racism and sexism of that time are bound to the same discoveries I can’t help romanticising. I try to hold the cruelty and the wonder at once, because pretending it was all one or the other feels dishonest, and there’s something to learn from both. That’s what I tried to do as I walked deeper into the gallery. In the main hall, two tall pendulum clocks stood with dark wooden frames and brass hands. They’d been used to mark the exact moment Venus touched the edge of the Sun. The one on the left had belonged to John Winthrop, Harvard’s second professor of mathematics and natural philosophy. His clock was no match for the precision instruments in London, but it was the best Boston could offer at the time. Scientists were crossing borders and setting aside politics, all for a chance to measure the same passing shadow Finding a good clock was the least of Winthrop’s problems. Before anything else, he had to get himself to Newfoundland – one of the few places from which the 1761 transit would be visible. That meant securing permission and funding for the trip, neither of which came easily. Harvard, to Europeans, was still a provincial college, and Winthrop had no personal fortune to fall back on. Worse, Massachusetts was a British colony in the middle of the French and Indian War, and his planned route cut straight through an active war zone. With help from his former student James Bowdoin, a member of the Massachusetts General Court, Winthrop managed to convince the British royal governor and the colonial assembly to back his voyage. They arranged a transport ship and letters of safe passage addressed to both British and French commanders. Somehow, it worked. Winthrop became the westernmost observer of the 1761 transit, collecting data in the middle of a war. And he wasn’t alone. Across the world, scientists were crossing borders and setting aside politics, all for a chance to measure the same passing shadow. On the other side of the world, the Seven Years War was raging across all of Europe and its colonies. Just days into their voyage to Sumatra to observe the transit of Venus, Charles Mason and Jeremiah Dixon’s ship was attacked before these English astronomers’ letter of safe passage could even be read; there wasn’t exactly a protocol for ‘Please don’t shoot, we’re here for science.’ But when they informed the Royal Society that they were abandoning the mission, the response was less than sympathetic. They were threatened with disgrace and legal action unless they continued. So, at what felt like a literal dead end, they started writing letters to anyone who would listen. Eventually, they were granted permission to observe the transit from the Cape of Good Hope, near present-day Cape Town, South Africa. Even for those who reached their original destinations, things didn’t always go according to plan. Guillaume Le Gentil, a French astronomer, had set out the year before to observe the 1761 transit from Pondicherry, in India, but his ship was blown off course and, by the time it neared the coast, the British had seized the city. The transit came and went while Le Gentil was still at sea, his instruments useless on a rocking deck. Rather than head home, he stayed in the region for the next transit, eight years later. When he finally returned to Pondicherry, by then reclaimed by the French, he built an observatory, and waited. But on the morning of 3 June 1769, clouds covered the Sun at the crucial moment. When Le Gentil made it back to France in 1771, his job was gone, his wife had remarried, and his estate had been carved up by relatives. Two chances, 11 years, and not a single usable measurement to show for it. I didn’t feel sorry for him one bit. Reading about these expeditions, it was hard not to see how warped it all was: colonists granting one another permission to work on land that wasn’t theirs, while the people who actually lived there were written off as primitive or irrelevant. I kept thinking about the knowledge systems that existed alongside these expeditions, and the ways of understanding the sky that never made it into European reports. That thought became more personal when I read about Le Gentil’s expedition, because Pondicherry was not some distant point on a map. It was a town in southern India, not far from where I grew up. The place still carries traces of that history: pastel French villas, narrow streets with European names, even the colonial version of its name, altered from Puducherry into something French tongues could say more easily. A whole town rewritten to sound foreign. But colonialism didn’t just rename cities. It rewrote knowledge. It buried scientific traditions that already existed, and replaced them with its own. I grew up hearing my mother recite the Hanuman Chalisa, a 16th-century shloka or devotional hymn that describes the god Hanuman flying toward the Sun as a child, mistaking it for a fruit. One verse has been interpreted as giving a distance from Earth to the Sun that’s astonishingly close to the modern value. I don’t believe a god literally flew to the Sun, and scholars still debate whether that reading is accurate; some argue that the units were later reinterpreted to fit current science. But whatever one makes of that number, it stayed with me. It suggested a world in which the Sun was not only an object of worship, but of calculation, speculation and close attention. I believe Indian astronomers understood far more than they are often given credit for, and that some of their methods and insights were lost or pushed aside, beneath the colonial versions that took their place. So no, I don’t feel sorry for these scientists or their bad luck. What I can admire is the stamina: wars, storms, months at sea, all for a few hours of observation. The instruments around me, most of them brass, were glinting under the lights. Some were so small I could have carried them in my hand; the largest stood right beside me, a Gregorian reflector crafted in London and used by Winthrop to observe the 1769 transit of Venus, right here in Cambridge, MA. By the time the 1769 transit came around, the colonies had changed. Tensions with Britain were boiling over, and Harvard, once an outpost of royal science, had turned into a hotbed of rebellion. British goods were being boycotted and royal authority was crumbling. In 1764, Harvard Hall caught fire after someone left a hearth unattended. The blaze took the college library and most of Winthrop’s instruments from the 1761 transit with it. By the time the smoke cleared, the observatory was gone and the next rare alignment was already on its way. So Winthrop and other American scientists wrote to the British, asking for help. And somehow, it worked. Despite all the political chaos, instruments and equipment kept arriving from London, taxes paid and customs waived, as if revolution wasn’t brewing outside. Most of what surrounded me in that museum had once been part of that shipment, including the reflector in front of me. Instead of appearing as a clean, crisp dot, Venus seemed to cling to the edge of the Sun, forming a dark teardrop I was standing in a room filled with centuries of human curiosity. ‘People who were directly at war still wrote nice letters to each other saying: “May I come into your territory, and can you help supply funding, canoes and instruments?”’ said Sara Schechner, curator of the gallery. ‘And the reply would be something like: “Well, maybe – but I don’t have a lot of money to spare. I’m buying guns to shoot at you on the other side.” The fact that it’s a real conversation is amazing.’ Letters were written to monarchs and governors, begging for funding and safe passage. Expeditions were launched to the far corners of the Earth, armed with telescopes, transit clocks, and an urgency usually reserved for war. But even as empires clashed, science and curiosity were allowed to slip through the cracks of politics. Men sailed for months, lost sleep, got scurvy, missed their children’s births, and even put a pause on the thing they love most, war, all just to watch Venus cross the Sun. This was science at its most romantic: ungovernable, impractical, even dangerous. Those tiny measurements changed how we saw the solar system. They helped make the cosmos measurable through a single value, the astronomical unit: the distance from Earth to the Sun. Once that number was known, the relative distances of the planets could be converted into real ones. The solar system transformed from a diagram to a scale model. Earth’s place in the Universe, once guessed at by instinct and scripture, could now be calculated in kilometres. The 1761 and 1769 transits didn’t deliver perfect results. Observers were plagued by weather, inconsistent instruments and something they hadn’t anticipated: the black drop effect. Instead of appearing as a clean, crisp dot, Venus seemed to cling to the edge of the Sun, forming a dark teardrop that blurred the moment of contact. That blur mattered because astronomers needed to time the exact moments when Venus touched the Sun’s edge and then fully crossed onto its face. The black drop effect smeared those contact points, making the measurements too uncertain for the precise parallax calculation they hoped to make: comparing observations from different places on Earth to determine exactly how far away the Sun was. But the effort still changed everything. It offered a new vision of science dependent on observations gathered across the world, stitched together by shared purpose. ‘It was a true collaboration,’ Schechner says. There was ambition, yes, but also trust, generosity and a willingness to let curiosity matter more than rivalry. The 19th century brought refinement. When Venus returned in 1874 and 1882, the world was newly connected – railroads spanned continents, telegraph lines carried near-instant messages, and photography had entered the astronomer’s toolkit. No longer dependent on a watchful eye and a swinging pendulum, scientists could capture the transit frame by frame and measure it at leisure in the lab. The black drop effect still lingered, but photographic plates blunted its influence, allowing astronomers to pin down the astronomical unit at 149.59 million km, astonishingly close to the value accepted today. By the 20th century, radar and space-based observations had taken over planetary science. The transits were no longer scientific emergencies but public spectacles. When Venus crossed the Sun again in 2004, NASA streamed it live, but Schechner wanted something older, closer to faith than technology. She restored Winthrop’s 1769 telescope and gathered people to watch through it as Venus moved across the Sun. In the process, she met Kenneth Launie, the engineer who helped bring the instrument back to life. Eight years later, when Venus crossed the Sun for the last time this century, Launie proposed. Their wedding brought the planet into everything, from the canopy to the cake. It was another version of the story I had been tracing through the museum: people folding their lives around a planet, treating curiosity as something worth loving. We’ve lost the sense that science can be an object of beauty in itself, not just a tool for achieving results The next transit of Venus will happen in 2117. I won’t be there to see it. Most of us won’t. Maybe someone will stand in the same museum, staring at the same clocks and telescopes, wondering what all the fuss was about. Or maybe they will set up a camera in their backyard and try to catch a glimpse. Maybe the skies will be too clouded by smoke, and the kind of light we can’t see through anymore, and we’ll know, with greater precision than ever, exactly where Venus is, but won’t be able to see her. Perhaps governments will have tightened their grip on science so much that a curious person with a telescope in their backyard would be seen as a problem. What has changed since the 18th century that makes us even wonder about that? I think what’s missing is the obsession, the sense of wonder that made those expeditions feel like cultural events rather than technical exercises. The instruments around me in the gallery made this contrast sharp. The telescopes and clocks of the 18th century were made of warm brass and wood, etched with flourishes and gilded corners that served no functional purpose except to be beautiful. Today’s instruments are made of cold steel and glass, efficient and practical. Perhaps that’s progress, but perhaps it’s also part of what we’ve lost – the sense that science can be an object of beauty in itself, not just a tool for achieving results. Science held a place in the heart as well as the mind. Of course, the 18th century was far from idyllic. Wars raged across continents, colonies were exploited, and imperialism was expanding. In many ways, we live in a better time. And yet, what strikes me is that even in the middle of those horrors, they got one thing right: they treated curiosity as something worth everything. They put aside rivalries and risked their lives for it. Today, our wars are quieter, our politics less deadly, at least here in the United States, but we can’t seem to agree to put science ahead even within our own borders. The hunger that once bent empires toward the sky feels like it has thinned out. As Richard Feynman once said, science does not diminish beauty but adds to it: a flower is not less lovely because we know about the cells in its petals, the pigments that evolved to attract bees, or the physics of light scattering on its surface. If anything, those layers of knowledge deepen the wonder. The same is true for Venus. The transits were never just about the astronomical unit, but the fact that knowledge could enhance the beauty of the world. And maybe that’s the lesson left to us. That curiosity itself can be enough – that science doesn’t have to justify itself with utility or profit to matter. The astronomers who chased Venus risked everything not because it would make their lives easier, but because they couldn’t bear not to know. I keep returning to the joke that first pulled me in: the clearest example I have found for why science should be romantic is Venus, the goddess of love herself. I have become a little obsessed with her transits too – not for the measurements, but for what they reveal about the longing beneath science: the desire to make the Universe measurable, intimate and beautiful. Maybe when Venus crosses the Sun again in 2117, some of that romance will return. I hope we find it sooner.