When thirty-three-year-old Richard Carrington settled down to sketch sunspots on the morning of September 1, 1859, he could not have known that he was about to witness the most important change ever glimpsed in a cosmic environment. His career, once so promising, seemed to be slipping away. The son of a successful brewer, at the young age of twenty-five, he had gained entry to the Royal Astronomical Society, and shortly thereafter he had built his own observatory. There, over the next three years, he created a catalog of precise stellar measurements that was so immediately useful to navigators that the Lords of the Admiralty directed it be printed at public expense. The discovery of the solar cycle now moved Carrington to undertake a rigorous study of sunspots that soon earned him a reputation as Britain’s premier solar observer.

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Before dawn on July 18, 1858, Carrington was suddenly called home. “In arriving,” he wrote to a colleague, “I…found my father no more.” It fell to him to manage the family brewery. The work gave him the money he needed to sustain his career, but it also consumed the time he needed to stay at the forefront of solar astronomy. On the first morning of September 1859, Carrington must have felt that solar observation was a luxury he could not count on for much longer.

Then, at exactly 11:18 AM, something changed on the solar surface. “There suddenly broke out,” Carrington wrote, “…a kind of conflagration,” which for two full minutes outshone the rest of the Sun. He quickly suspected that he had witnessed a flare of previously inconceivable power. Seeking independent confirmation, he visited a colleague at Kew Observatory, near his brewery. He learned that the observatory’s magnetic instruments had recorded a minor disturbance in Earth’s magnetic field at exactly the moment that he had seen the flare. About eighteen hours later, brilliant, blood-red auroras surged toward Earth’s equator. Electric telegraph lines across Europe and the Americas shorted out. Other lines worked even when switched off.

Each storm sparked a wave of scientific inquiry, until, in the early twentieth century, scientists finally understood why electrifying societies had grown precariously vulnerable to environmental upheavals on the Sun.

The “Carrington Event,” as it came to be known, could not rescue Carrington’s career, but it did secure his immortality in the annals of science. It suggested the existence of a profound, previously hidden connection between sudden environmental changes on the Sun and on Earth. The connection was perceptible in 1859 because previous discoveries of the Sun’s variable influence on climate had fostered the development of solar science. It seemed important because it appeared capable of disrupting new electrified communication and transportation networks that were beginning to give industrializing countries unprecedented control over terrestrial environments. For the rest of the nineteenth century and into the twentieth century, magnetic storms, triggered by colossal solar explosions, repeatedly disrupted those networks. Each storm sparked a wave of scientific inquiry, until, in the early twentieth century, scientists finally understood why electrifying societies had grown precariously vulnerable to environmental upheavals on the Sun.

Coronal Mass Ejections and Magnetic Storms

The storms that disrupted nineteenth-century infrastructure on Earth had their origins deep within the Sun. Such storms occur when a vast interior region of the Sun that is too hot for convection collides with the cooler region nearer the Sun’s surface, creating a magnetic field of unimaginable power. The magnetic field arcs above the solar surface into the billowing solar corona, where temperatures reach an extraordinary 20 million degrees Celsius. In this frenzied heat, about one million tons of charged particles careen into space every second. This solar wind thins as it races ever farther from the Sun, but even around Earth up to ten trillion particles pass through every square meter of space every second. Because these particles are charged, the solar wind extends the Sun’s magnetic field into interplanetary space. When the Sun travels through a relatively empty expanse between stars, as it has for some two million years, then it is only in the outer solar system that the pressure of the solar wind drops so low that it can no longer hold back the pressure of interstellar dust. Everything within the solar wind is inside the Sun’s extended atmosphere, known as the heliosphere, which means that, in a sense, Earth orbits through the Sun itself.

The energetic particles of the solar wind would wreak havoc on terrestrial life were it not for the constant sloshing of molten iron in Earth’s outer core. There, interactions between streams of liquid iron generate a magnetic field one quintillion times more powerful than that of an ordinary lab magnet (but thousands of times weaker than the Sun’s). Earth’s magnetic field radiates from our planet’s poles, arcs deep into space, and creates a vast, magnetic bubble, known as the magnetosphere, that protects us from the solar wind.

But Earth’s inner dynamo does not provide a perfect defense. The solar wind smashes into the leading edge of Earth’s magnetosphere with supersonic speed, creating a shockwave that can come closer than one hundred thousand kilometers to the planet’s illuminated side. The wind then sweeps past Earth along a magnetotail, an extension of Earth’s magnetic field away from the Sun, that can be millions of kilometers long. When the magnetic fields of Earth and the solar wind point in opposite directions, they can link at points of contact on either the shockwave or the trailing edge of the magnetotail, opening a portal directly to the Sun’s corona. Charged particles originating from the corona surge into the gap but are soon snared by two great magnetic loops—the Van Allen Radiation Belts—that usually keep them from Earth’s surface.

Even these belts do not offer complete protection. A new magnetic flux continually arises within the Sun and surges into the corona. Convection within the Sun and the differential rotation of the Sun’s surface warp the coronal magnetic field, as do links to the interplanetary field created by the solar wind. The coronal magnetic field is therefore constantly under immense strain, and when that strain becomes too great, its tangled magnetic field lines snap open. The result can be an eruptive solar flare: a colossal release of electromagnetic energy. The most powerful flares usually detonate from large sunspot groups, where the Sun’s magnetic field can be a million times stronger than Earth’s. Gigantic magnetic bubbles also break free from the Sun as the solar magnetic field reconfigures, launching up to fifty billion tons of plasma into interplanetary space. Powerful flares may accompany the departure of these coronal mass ejections (CMEs); both are examples of solar storms.

Electromagnetic emissions from flares travel at light speed and therefore reach Earth in around eight minutes. Radio signals then rush through Earth’s atmosphere. X-ray and extreme ultraviolet emissions enhance the ionization of the ionosphere, the layer of the upper atmosphere charged by solar radiation.

Several minutes later, electrons and protons may arrive in enormous quantities, dramatically increasing radiation in Earth’s magnetosphere.

CMEs, meanwhile, hurtle through space at up to three thousand kilometers per second. Most take several days to travel Earth’s distance from the Sun, and the overwhelming majority sail harmlessly into the outer solar system. Some, however, collide with Earth’s magnetic field. When the lines of a CME’s magnetic field and those of the Earth’s magnetic field are pointed in the opposite directions, the CME can unite with the Earth’s magnetosphere and fill it with vast quantities of solar energy. The result is a geomagnetic storm that amplifies the ionospheric and radio disruptions caused by flares and saturates the radiation belts surrounding Earth to such an extent that new belts can suddenly form. The density of the upper atmosphere also changes at midlatitudes, while magnetic substorms explosively release stored magnetic energy. Geomagnetically induced currents—or GICs—surge across Earth’s surface. The auroras intensify, expand toward the equator, and often turn a vivid blood red. Because Earth’s magnetic field is twice as intense around the poles as it is at the equator, the magnetic consequences of a solar storm are far greater at higher latitudes.

Arctic Climates, Solar Changes, and Big Data

For some three hundred thousand years, auroras were the only signs of geomagnetic storms that human populations noticed. Then, in the thirteenth century, refinements to an ancient technology, the compass, led to its widespread adoption by sailors. No doubt some sailors noticed that compass needles no longer pointed toward the magnetic north pole during auroras. This was the first way in which geomagnetic storms disrupted transportation technology. Early in the eighteenth century, scholars first described in writing the correlation between auroras and erratic compass movements, but they had no way of knowing that environmental changes on the Sun were the cause. Later that century the rising importance of waterborne commerce for Europe’s maritime powers helped motivate efforts to map Earth’s magnetic field. If they had precise knowledge of the continually shifting difference between the magnetic and geographic north poles at every point of their journey, sailors would be able to use their compasses more effectively for navigation. The Prussian baron Alexander von Humboldt carried out the best-known of these mapping efforts in Central and South America. When he returned home, he resolved to study how magnetic fields changed across space and time. He was measuring shifts in magnetic declination—the angle between geographic and magnetic north poles—in a shed outside Berlin when, on December 21, 1806, his compass needles started moving erratically just as auroras danced across the sky. Humboldt coined the term “magnetic storm” to describe the magnetic disturbances that auroras seemed to cause.

It was a change in the influence of the Sun on climate that would begin to clarify the connection between solar changes and magnetic storms. Sulfuric aerosols trapped in ice cores suggest that a truly massive volcanic eruption took place in 1809, followed by a succession of smaller eruptions that culminated in the staggering explosion of Mount Tambora in 1815. All of these eruptions in a period of low solar activity sent average global temperatures plummeting to lows they had never reached before during the LIA. Records from that period indicate the climatic effects. Arctic explorers, such as the British whaler William Scoresby, struggled to navigate expanding sea ice. In 1816 the stratosphere was saturated with Tambora’s dust, and sea ice nearly wrecked Scoresby’s ship off the eastern coast of Greenland. Yet in the following year Scoresby reported “a remarkable diminution of the polar ice” in the same location. Climatologists now know that volcanic dust was beginning to fall out of the atmosphere at that point, but marine sediments, tree rings, and other evidence extracted from archives of nature suggest that Arctic temperatures had not recovered. Instead, the continued influence of Tambora may have affected atmospheric pressure in the northern Atlantic Ocean, altering wind patterns to push sea ice from the Greenlandic coast. If so, Scoresby unwittingly described the effects of a shift in the quantity of solar radiation that reached Earth’s surface.

According to the historian of science Vidar Enebakk, Scoresby’s report intrigued proponents of scientific discovery and Arctic exploration. Soon they had ample motivation to join forces in exploiting the apparent thawing of the far north. The Northwest Passage Act, which offered a reward to any Briton who could chart a shipping route through Arctic Canada to Asia, had been repealed in 1818. Its replacement, the Longitude Act, which incentivized both polar exploration and improvements to navigation, had the effect of aligning the goals of scientific and military personnel. As a side effect, it elevated officers in the Royal Artillery, the Royal Engineers, and the Admiralty Hydrographic Office, whose expertise in precise measurement suddenly seemed essential in voyages of polar exploration. One participant was a young Irish officer named Edward Sabine.

In 1819 Sabine joined a crew aboard the Hecla, a refitted “bomb vessel”—a ship armed with mortars—that, like others in its class, had been named after a volcano. Off the coast of Baffin Island, the crew approached the magnetic north pole, where Sabine took measurements of the intensity and inclination of the local magnetic field. It was the beginning of a lifelong obsession. Over the next two decades, his magnetic measurements would take Sabine from Brazil to Svalbard, a Norwegian archipelago on the edge of the Arctic Ocean. Eventually he assumed a leading role within the “magnetic lobby,” a group of influential scientists and naval officers who recognized the practical and scientific potential of measuring Earth’s fluctuating magnetic field. Owing in large part to Sabine, the British government financed the construction of magnetic observatories around the empire. Because John Herschel believed that the correlation between magnetic storms and auroras revealed both to be meteorological phenomena, the new observatories would be equipped with weather instruments that, in time, would permit the first global measurements of climate change.

Sabine would soon mastermind the largest scientific enterprise of his era. From 1839 to 1857, his observatories, equipped with magnetometers and other measuring devices, operated around the clock, six days a week (they closed on Sundays). An unprecedented torrent of environmental data flowed into Sabine’s “magnetic department” in Woolwich. There, Sabine led a team of mathematicians—women and men known as “computers”—who tabulated and analyzed measurements on a scale that would have been difficult to imagine in an earlier age.

Sabine’s wife, Elizabeth Leeves, was a scientist in her own right. In the 1850s she translated Humboldt’s Cosmos, a sweeping compendium that popularized the discovery of the sunspot cycle. When Leeves introduced the cycle to Sabine, he realized to his astonishment that it precisely matched a mysterious pattern in the magnetic disturbances he had charted with his computers. The correlation seemed to suggest that space was alive with invisible forces that bound together the variable environments of the Sun and Earth.

“We stand on the verge of a vast cosmical discovery,” John Herschel wrote after hearing the news, “such as nothing hitherto imagined can compare with.”

New Vulnerabilities, New Discoveries

Scientists like Sabine, Leeves, and Herschel also stood on the threshold of modernity. Perhaps above all, the new era involved the rapid expansion and growth in density of networks that enabled unprecedented movement of commodities, people, information (including the measurements recorded by Sabine’s observatories), and invasive organisms. Those networks, powered in the late eighteenth century by wind (for most waterborne transportation), muscle (for most land transportation), and, increasingly, light (for emerging telegraph networks), were revolutionized in the nineteenth century by the widespread exploitation of fossil fuels and, before long, electricity. Electric telegraph lines and railroads encouraged and were encouraged by a new age of imperial expansion, commodity extraction, industrialization, urban growth, global migration, rising population, and scientific development, among other things. The world was coming together, economically, culturally, and biologically, but it was doing so through the self-serving machinations of imperial governments in a handful of wealthy cities.

A unique combination of solar environmental changes, climatic disruptions, magnetic storms, technological advancements, and astronomers being in the right place at the right time had revealed a previously hidden connection between the Sun and Earth.

In deeply unequal ways, the new era of networked industrialization and electrification began to alleviate the conditions of scarcity that had rendered many communities so vulnerable to the climatic disruptions of the LIA. The Carrington Event in 1859, though, suggested that the networks responsible for increasing the resilience of populations in the face of changes in the Sun’s influence on climate also made those populations vulnerable to mysterious solar fluctuations that had previously merely illuminated the night sky. Meanwhile, as we have seen, monsoon failures suggested to some British scientists that the imperial periphery remained at the mercy of the Sun’s influence on weather, with potentially dire consequences for the empire as a whole.

While undertaking a magnetic survey of the Indian subcontinent, Colonel Alexander Strange of the Royal Artillery had experienced firsthand the human toll of drought. In 1872, as drought ravaged India, he proposed that the British government finance the construction of a unique, nationally funded laboratory. Among other things, it would maintain continuous surveillance of the Sun, using a spectroscope, an instrument that disperses light into its constituent colors to reveal the chemical properties of its source. Strange hoped that spectroscopic surveillance could predict the Sun’s influence on weather, which he thought could aid efforts to avoid another horrific famine in India.

Strange wanted a facility separate from the Royal Observatory at Greenwich because he felt that the observatory’s director, George Airy, no longer understood how astronomy could serve the state. It was a common refrain among British scientists of the nineteenth century, many of whom sought to create new institutions for specialized disciplines or else reform old ones to be more inclusive and responsive to advances in scholarship. By the 1870s many astronomers had flocked to the exciting frontier that the techniques of spectral analysis (called the “physics of astronomy,” or astrophysics) seemed to open in the new astronomy. The aging Airy had devoted his observatory to stellar measurements that now produced trifling improvements to navigation. By aiding mariners, Airy believed, such measurements provided a tangible service to the state that the newfangled spectroscopy might not be able to match. Still, he was savvy enough to forestall Strange’s challenge to his authority. He undermined support for a new observatory by introducing a program of solar photography and spectroscopy at the Royal Observatory.

In 1873 twenty-two-year-old Edward Walter Maunder was hired as the spectroscopic assistant for this program. The son of a Wesleyan minister, Maunder had attended King’s College London, a working-class alternative to Oxford and Cambridge. As a teenager he had once glimpsed the Sun “low down in the west, shining red through the mist,” he later recalled, and noticed “a round black spot, just as if a nail had been driven into him up to the head.” The next time he saw the Sun just above the horizon, that sunspot had moved, and on the following occasion it was gone. Maunder, enthralled, would devote the rest of his life to the study of the Sun.

On a foggy November morning in 1882, Maunder noticed another, even bigger spot on the crimson Sun. It was so obvious that soldiers marching nearby pointed it out to one another. Using the spectroscope, Maunder detected a hydrogen flare arcing out from the sunspot. That night the telegraph network near London collapsed while an aurora lit up the sky. When he discovered the next morning that a magnetic disturbance had been measured at Greenwich, Maunder resolved to find the statistical relationship between sunspots and magnetic storms that had long eluded solar astronomers.

Maunder soon found that even big sunspots did not always coincide with magnetic storms. He wondered whether sunspots could launch their magnetism into space through flares. Earth, a tiny target in the vastness of space, would often be spared from being hit by these magnetic projectiles. The science author Stuart Clark notes that the concept was nonsensical to contemporary scientists, who assumed that magnetism could not break free from a magnet and that the Sun’s energy radiated equally across its surface.

After seventeen years at the Royal Observatory, Maunder was finally allowed an assistant. Influenced by the progressive Methodist faith in which he was raised, Maunder was one of his profession’s most outspoken advocates for women’s participation in science. He hired the first woman ever employed by the Royal Observatory: a brilliant computer named Annie Russell, who soon proved his equal in solar astronomy. United by their shared fascination with the Sun’s environmental changes, Annie and Walter wed in 1895.

Annie was then forced to resign from her job, because married women were not allowed to hold positions in the civil service. Nevertheless, she continued her work. Among other things, she refined methods for photographing the solar corona during eclipses. After studying her pictures, Walter realized that the corona was not homogeneous. Instead it was full of the magnetized structures he had proposed earlier. Then in 1903 a mammoth sunspot failed to cause a large storm, but a smaller spot coincided with one so massive that, as one solar astronomer put it, “practically the world’s whole telegraph system was upset.” In a foreshadowing of graver threats to come, this time GICs also disrupted the electrical signals that powered the rail network in London and surged through telephone lines around Chicago.

In response, the Maunders pored through reams of sunspot and magnetic observations until they found the correlation that established the causation solar astronomers had long sought. Magnetic storms, they realized, followed a twenty-seven-day cycle, matching the Sun’s rotation. During every storm, a sunspot had revolved into position near the apparent center of the solar surface, like the turret of a battleship lining up its target. Drawing on an idea proposed by the Swedish physicist and chemist Svante Arrhenius, Walter suggested that rays of charged particles might shoot out of sunspots and smash into Earth. This theory gradually won widespread acceptance—although it would be another seventy years before instruments in space revealed the magnetic bubbles, not rays, that we today call coronal mass ejections.

A unique combination of solar environmental changes, climatic disruptions, magnetic storms, technological advancements, and astronomers being in the right place at the right time had revealed a previously hidden connection between the Sun and Earth. This connection would become increasingly important over the twentieth century, as the rapid development of technological infrastructure created ever-expanding and increasingly dangerous sensitivities to geomagnetic storms.

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Excerpted from Ripples on the Cosmic Ocean: An Environmental History of Our Place in the Solar System by Dagomar Degroot. Copyright © 2025. Available from Harvard University Press.