The Carrington Event was the most powerful solar storm to hit Earth since the beginning of the industrial age. On September 1-2, 1859, a massive eruption from the sun sent a wave of charged particles slamming into Earth’s magnetic field, producing auroras visible as far south as Hawaii and Colombia, and knocking out telegraph systems across North America and Europe. It remains the benchmark scientists use when modeling worst-case scenarios for space weather.
What Happened in September 1859
On the morning of September 1, 1859, British astronomer Richard Carrington was sketching sunspots through his telescope when he noticed something no one had ever documented before: a brilliant white-light flare erupting from the sun’s surface. Another observer, Richard Hodgson, independently witnessed the same flash from a separate location in England. Within minutes, magnetic instruments on the ground registered a sudden pulse, and less than 18 hours later, a massive cloud of solar material reached Earth.
That transit time was remarkably fast. Coronal mass ejections, the billion-ton clouds of magnetized plasma the sun occasionally hurls into space, typically take two to three days to cross the 93-million-mile gap. The 1859 ejection covered that distance in roughly 17.6 hours, likely because an earlier eruption had cleared the way through the solar wind, reducing drag for the second blast.
When the cloud hit Earth’s magnetic field on September 2, the resulting geomagnetic storm was unlike anything in recorded history. Magnetometer readings in Bombay, India, captured a magnetic field disturbance of 1,600 nanoTesla, an enormous swing. Scientists have estimated the storm’s overall intensity at a Dst index of roughly negative 850 nT, a measure of how much Earth’s magnetic field was compressed and distorted. For context, anything below negative 250 nT qualifies as a “great” geomagnetic storm.
Auroras at the Equator, Fires on the Wires
The most visually stunning effect was the aurora. Normally confined to high-latitude regions near the Arctic and Antarctic, the northern and southern lights pushed toward the equator. Ship logs from the Caribbean recorded auroral displays at latitudes as low as 12 degrees north, roughly the latitude of Barbados. Observers in Hawaii and Santiago, Chile (around 23 degrees magnetic latitude) also reported vivid curtains of color in the sky. People in the northeastern United States reportedly could read newspapers by the red and green glow at midnight.
The technological damage, modest by today’s standards, was dramatic for the era. Telegraph networks across North America and Europe experienced widespread failures on September 2 and 3. The storm induced powerful electrical currents in the long metal wires, causing sparks that set telegraph paper on fire, delivered shocks to operators, and overwhelmed equipment. The Boston Globe reported on September 3 that “there was a great magnetic storm which affected all the telegraph lines in the country,” with some lines so badly damaged they took days to repair. There were also scattered reports of people receiving shocks from doorknobs and other metal objects as currents surged through anything conductive.
Why the Carrington Event Still Matters
In 1859, the telegraph was the only electrical infrastructure at risk. Today, a storm of the same magnitude would interact with a vastly more complex web of technology: continental power grids, communications satellites, GPS navigation, undersea internet cables, and aviation electronics. The U.S. Geological Survey has warned that an event of that magnitude could stress or destroy high-voltage transformers across the United States, particularly in the Midwest and along the East Coast. These transformers are expensive, custom-built, and can take months or even years to replace.
A detailed risk assessment published in the journal Risk Analysis modeled the impact of a Carrington-scale storm on the United Kingdom alone. Without any advance warning, such a storm could disrupt power for more than 60 million people and nearly 30 million workers, with economic losses reaching £15.9 billion (roughly $20 billion). With current space weather forecasting, those numbers drop significantly: about 19 million people affected and losses closer to £2.9 billion. Enhanced forecasting could reduce the toll further still, to around 8 million affected and under £1 billion in losses. The takeaway is that early warning buys time for grid operators to take protective measures like temporarily disconnecting vulnerable transformers.
Blackouts from a superstorm wouldn’t be like a neighborhood losing power in a thunderstorm. Entire regions could go dark simultaneously, and the cascading effects on water treatment, hospital systems, refrigeration, fuel pumps, and financial networks would compound quickly. USGS geophysicist Jeffrey Love has noted that “an intense magnetic storm could be far more hazardous than what the electric power transmission industry is prepared for.”
How Likely Is a Repeat?
More likely than most people assume. Physicist Pete Riley of Predictive Science Inc. analyzed records of solar storms spanning more than 50 years and calculated that the probability of a Carrington-class event hitting Earth within any given decade is approximately 12 to 13 percent. Those odds are comparable to rolling a specific number on a pair of dice within a few throws. Over a human lifetime, the cumulative probability becomes substantial.
Earth has already had close calls. In July 2012, a coronal mass ejection at least as powerful as the 1859 event tore through Earth’s orbital path, missing the planet by about a week’s worth of orbital travel. Had it erupted nine days earlier, it would have scored a direct hit. The 1989 geomagnetic storm, far weaker than Carrington-class, was still strong enough to collapse the Hydro-Québec power grid and leave six million Canadians without electricity for nine hours.
Events Far Larger Than Carrington
The Carrington Event is the strongest storm humans have experienced in the modern era, but it is not the strongest the sun has ever produced. Scientists have identified at least 10 ancient “Miyake events” by examining tree rings and ice cores. When extremely energetic solar particles strike Earth’s atmosphere, they produce a spike in a radioactive form of carbon (carbon-14) that gets absorbed by living trees and a spike in beryllium-10 that settles into polar ice. By counting tree rings and cross-referencing ice core layers, researchers can pinpoint when these bursts occurred.
The largest Miyake event discovered so far dates to approximately 14,300 years ago, identified in subfossil trees buried along the Drouzet River in France. That event was roughly twice the size of the next-largest known Miyake event (from the year 774 CE) and an order of magnitude more powerful than the Carrington Event. Researcher Edouard Bard described the radiocarbon spikes as “completely unprecedented.” If a Miyake-scale event struck today, the consequences would dwarf any scenario currently modeled for grid resilience. The sun, it turns out, is capable of far more than the worst we have personally witnessed.