Just after 11 o’clock on the morning of September 1, 1859, an English astronomer named Richard Carrington was sketching sunspots when two blinding white spots of light flared up in the middle of them. He ran to find someone to show, and by the time he got back about a minute later, the light was already fading. Five minutes after it started, it was gone. Within a day, skies from Canada to Cuba glowed red and green, gold miners in the Rocky Mountains got up to make breakfast in the middle of the night, and telegraph lines across Europe and North America sparked and shocked their operators. It was the biggest solar storm ever recorded, and it is now called the Carrington Event. Here is what happened, why it took a lucky astronomer to notice, and what a storm like it would do to a world that runs on satellites and power lines.
Five minutes that changed astronomy
Carrington was 33 and ran his own observatory at Redhill, south of London. He had set himself a long, patient job: tracking every sunspot through a full 11-year solar cycle to work out exactly how the Sun rotates. He never looked at the Sun directly. His telescope projected an image of it, about 11 inches wide, onto a plate of glass coated with a pale straw-colored paint, and he traced the spots by hand.
That morning, he was timing spots against crosshairs when “two patches of intensely bright and white light broke out” inside a huge sunspot group. His first thought was that a ray of sunlight had slipped through a hole in the screen. He moved the image, and the patches moved with it. They were on the Sun. “Being somewhat flurried by the surprise,” he wrote, “I hastily ran to call some one to witness the exhibition with me.” When he got back within 60 seconds, he was “mortified” to find the light already fading. In those five minutes, he calculated, the patches had moved about 35,000 miles.
He was not the only witness. Richard Hodgson, another amateur astronomer in London, saw “a very brilliant star of light” in the same spot at the same time. Their two reports were published side by side that November. Together they are the first recorded sighting of a solar flare, a sudden explosion of energy in the Sun’s magnetic field near a sunspot. Flares this bright are almost never visible in ordinary white light, which is why nobody had noticed one before.
There was one more clue. At Kew Observatory near London, a magnetometer, an instrument that tracks tiny changes in Earth’s magnetic field, jumped at the same moment the flare appeared. Carrington suspected a link between what he saw and what happened next, but he was careful. “One swallow does not make a summer,” he wrote.
The night the sky caught fire
About 17 and a half hours after the flare, a giant cloud of magnetized gas from the Sun slammed into Earth. Scientists now call this a coronal mass ejection, or CME. Most CMEs take several days to cross the 93 million miles between the Sun and Earth. This one was unusually fast, probably because an earlier eruption a few days before had swept the path clear.
When it hit, it shook Earth’s magnetic field hard. The aurora, normally a sight for the far north and far south, spread across most of the planet. People saw it in Cuba, Hawaii, southern Mexico, and as far toward the equator as Colombia. In the northeastern United States, people reported that they could read a newspaper by its light. In the Rockies, the glow was bright enough to wake gold miners, who started making breakfast because they thought it was morning.
A Baltimore paper described the display that week as a light that “appeared to cover the whole firmament, apparently like a luminous cloud,” brighter than a full moon. A gold digger in Victoria, Australia, remembered it 50 years later as “a sight never to be forgotten,” with colors streaming up from the southern sky and turning a rich purple overhead.
Telegraphs that ran without batteries
In 1859, the most advanced electrical network on Earth was the telegraph, the Victorian internet. It was strung across continents on long copper wires, and that turned out to be the problem. A rapidly changing magnetic field makes electric current flow in any long conductor, the same principle that makes a generator work. Every telegraph line became an antenna for the storm.
Across Europe and North America, telegraph systems failed. Operators reported sparks jumping from their equipment, and some got electric shocks. NASA notes that the storm set fire to some telegraph offices. Yet in a few places, the extra current was strong enough to use. On the night of September 2, operators on the line between Boston and Portland, Maine, disconnected their batteries entirely. “We are working with the auroral current,” the Boston operator tapped out. Portland answered that it was coming through “better than with our batteries on.” They kept sending messages for about two hours, powered only by the Sun.
How big was it, really?
Scientists rate geomagnetic storms with a number called Dst, which measures how much Earth’s magnetic field at the equator is weakened during a storm. The more negative it is, the worse the storm. Ordinary storms that put on an Arctic light show sit around −50 nanotesla. The storm that blacked out Quebec in 1989 reached about −589. Modern estimates for the Carrington Event range from about −800 to as low as −1,750. Nobody can pin it down exactly, because the magnetometers of 1859 often went off the charts.
It was not a one-off, either. A storm in May 1921 may have come close. Tree rings and ice cores record even bigger blasts in the distant past. A spike in radioactive carbon in tree rings from the year 774 points to a solar event that may have been ten or more times stronger than Carrington’s.
And in July 2012, a Carrington-class eruption crossed Earth’s orbit. It missed us because Earth was in a different part of its path around the Sun. Instead it hit NASA’s STEREO-A spacecraft, which measured it. “If it had hit, we would still be picking up the pieces,” space physicist Daniel Baker of the University of Colorado told NASA. He estimated that had the eruption come about a week earlier, Earth would have been in the line of fire.
What a Carrington storm would do now
In 1859, the damage was mostly limited to telegraphs. Today, the same physics reaches far more. Smaller storms give a preview.
Power grids. Long high-voltage power lines act like those telegraph wires. On March 13, 1989, a storm well short of Carrington’s tripped protective equipment on Hydro-Québec’s grid. The system collapsed in about 90 seconds, and millions of people in Quebec lost power for around nine hours. The real worry is large transformers, the house-sized machines at substations. Stray currents from a storm can overheat them, and replacements can take a year or more to build and deliver. Since 2016, U.S. utilities have had to study how their equipment would handle a severe solar storm under rules from the Federal Energy Regulatory Commission.
Satellites. A storm heats and puffs up the upper atmosphere, which adds drag on satellites in low orbits. In February 2022, a fairly moderate storm hit a day after SpaceX launched 49 new Starlink satellites into a low starting orbit. The extra drag was up to 50 percent higher than on earlier launches, and 38 of the satellites fell back and burned up. More satellites in orbit also means more to track, a problem that ties into the Kessler syndrome.
GPS. GPS signals pass through the ionosphere, the charged upper layer of the atmosphere, and a storm makes that layer lumpy and unpredictable. Receivers can lose lock or give positions that are off by many feet. If you want to know why a few feet matter, our explainer on how GPS finds you covers the timing involved.
A 2013 study by Lloyd’s of London and Atmospheric and Environmental Research estimated that a Carrington-size storm hitting the United States today could cost between $600 billion and $2.6 trillion, mostly from long power outages in the most exposed regions.
May 2024: a smaller test
On May 10, 2024, a large, very active sunspot group sent several CMEs toward Earth, and NOAA declared a G5, or “extreme,” geomagnetic storm, the first since 2003. It was nowhere near as strong as the Carrington Event, but it was the strongest in about two decades. Auroras were seen as far south as the Florida Keys, Puerto Rico, and Mexico’s Yucatán Peninsula, and millions of people saw the northern lights for the first time, often by pointing a phone camera at the sky.
The North American power grid came through in good shape, thanks in part to decades of planning since 1989. GPS was a different story. In the Midwest, it was the middle of corn-planting season, and many farmers rely on GPS-guided tractors that steer themselves to within an inch or so. During the storm, some guidance systems drifted or dropped out, and many farmers stopped planting until it passed. One later study found that GPS position errors reached up to about 230 feet in parts of the central United States, and agricultural economists have estimated that the planting delays cost farmers hundreds of millions of dollars.
Can we see the next one coming?
Much better than Carrington could. Spacecraft like NASA’s Solar Dynamics Observatory and the joint NASA and European Space Agency SOHO mission watch the Sun constantly, so forecasters can usually see a CME leave the Sun and estimate when it will arrive, often a day or more ahead. The final warning comes from satellites parked about a million miles toward the Sun, which measure the incoming cloud’s strength and magnetic direction, the details that decide how bad a storm will be, roughly 15 to 60 minutes before it hits.
That warning lets grid operators reduce loads and adjust their networks, and lets satellite operators protect their spacecraft. It does not tell anyone exactly when the next Carrington-size storm will come. One widely cited estimate put the odds of a storm that size hitting Earth in any given decade at about 12 percent. Other researchers, using different methods, have come up with lower numbers. Everyone agrees the chance is not zero.
The bottom line
For about five minutes in 1859, one careful observer happened to be looking at the right sunspot at the right moment. What he saw was a flare from an eruption that, a day later, lit up the skies of most of the planet and made the world’s first electrical network spark and catch fire. Nothing quite that big has hit Earth since, though one came close in 2012. The difference now is that we depend on long wires and satellites in almost every part of daily life, and that we are watching the Sun all the time. The next Carrington Event will not catch us by surprise. Whether it catches us unprepared is up to the people who build and run the grid.
Be ready for an outage, or read the whole story
Midland ER310 Emergency Crank Weather Radio — An AM/FM and NOAA weather-alert radio you can power by hand crank, a small solar panel, a rechargeable battery, or AA batteries, with a built-in flashlight and a USB port to top up a phone. Useful in any long outage, solar storm or not.
The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began — Stuart Clark’s history of the 1859 flare, the astronomers who were chasing the link between sunspots and Earth’s magnetism, and Carrington’s own strange and unhappy later life.