The Carrington Event was the most powerful magnetic storm ever recorded, reaching its peak on 1–2 September 1859 during solar cycle 10. It caused bright auroras seen around the world and led to sparks and fires in telegraph stations. This storm was likely caused by a coronal mass ejection (CME) from the Sun hitting Earth's magnetosphere.

The storm was linked to a very bright solar flare observed on 1 September 1859. British astronomers Richard Carrington and Richard Hodgson independently recorded this flare, marking the first known observations of a solar flare. A magnetic storm of this strength today could cause major electrical problems, power outages, and damage to the power grid.

History

On September 1 and 2, 1859, one of the largest magnetic storms ever recorded by ground-based instruments occurred. Scientists estimate the strength of the storm (measured as Dst) to be between −0.80 and −1.75 μT.

This storm is believed to have been caused by a burst of solar material, called a coronal mass ejection (CME), that traveled directly toward Earth. It took 17.6 hours to cover a distance of 150 million kilometers (93 million miles). Most CMEs take several days to reach Earth, but this one moved faster, possibly because a previous CME had already cleared the path of solar wind plasma, which may have been linked to a bright aurora observed on August 29.

On September 1, 1859, just before noon, two English astronomers, Richard Carrington and Richard Hodgson, independently recorded the first observations of a solar flare. They each wrote separate reports, which were published together in Monthly Notices of the Royal Astronomical Society. They also displayed their drawings of the event at a meeting of the Royal Astronomical Society in November 1859.

A Scottish physicist, Balfour Stewart, noticed a magnetic disturbance called a "magnetic crochet" in data from the Kew Observatory magnetometer. This, along with a magnetic storm observed the next day, led Carrington to suspect a connection between the Sun and Earth. However, he was unsure if the two events were related, writing, "one swallow does not make a summer." Later, American mathematician Elias Loomis collected and published worldwide reports about the 1859 storm, supporting the observations made by Carrington and Stewart.

Impact

Auroras were seen worldwide in both the northern and southern hemispheres. The aurora borealis over the Rocky Mountains in the United States was so bright that it woke up gold miners, who thought it was morning and began preparing breakfast. It was also reported that people in the northeastern United States could read a newspaper by the light of the aurora. The aurora was visible from the poles to areas near the equator, including south-central Mexico, Cuba, Hawaii, Queensland, southern Japan, China, New Zealand, and Colombia.

On Saturday, September 3, 1859, the Baltimore American and Commercial Advertiser reported that

Those who were out late on Thursday night saw another impressive display of auroral lights. The event was similar to one seen earlier, though the light was sometimes even brighter, and the rainbow colors were more varied and striking. The light seemed to cover the entire sky, like a glowing cloud through which the stars faintly shone. The brightness was greater than that of a full moon, but it had a soft and delicate quality that seemed to surround everything it touched. Between 12 and 1 a.m., when the display was at its peak, the quiet city streets under this unusual light looked both beautiful and strange.

In 1909, an Australian gold miner named C. F. Herbert described his observations in a letter to the Daily News in Perth:

I was mining for gold at Rokewood, about four miles from Rokewood township in Victoria. Myself and two friends saw a bright reflection in the southern sky at about 7 p.m. Within half an hour, a scene of extraordinary beauty appeared: Lights of every color seemed to come from the southern sky, one color fading to be replaced by another, sometimes even more beautiful. The lights rose toward the highest point in the sky, turning a rich purple there, and curled around, leaving a clear strip of sky that could be imagined as four fingers held at arm’s length. The northern side of the sky also had beautiful colors, curling around the highest point, but these were seen as a copy of the southern display, as the colors in both areas always matched. This was a sight never forgotten and was considered the most intense aurora ever recorded. Some saw it as a sign of nature’s beauty and the laws of the universe, while others feared it might signal a great disaster.

Because of electric currents caused by the aurora’s electromagnetic field, telegraph systems in Europe and North America failed, with some operators receiving electric shocks. Telegraph poles sparked. Some operators continued sending and receiving messages even after disconnecting their power supplies. The following conversation happened between two telegraph operators in the United States on the night of September 2, 1859, as reported in the Boston Evening Traveler:

Boston operator (to Portland operator): "Please disconnect your power source completely for fifteen minutes."

Portland operator: "Will do so. It is now disconnected."

Boston: "Mine is disconnected, and we are using the aurora’s current. How do you receive my writing?"

Portland: "Better than with our batteries on. The current comes and goes gradually."

Boston: "My current is very strong at times, and we can work better without batteries, as the aurora seems to cancel out and strengthen our batteries alternately, making the current too strong for our relay magnets. Let’s work without batteries while we are affected by this problem."

Portland: "Very well. Shall I go ahead with business?"

Boston: "Yes. Go ahead."

The conversation continued for about two hours using no battery power, relying only on the current from the aurora. This was the first time in history that more than a few words were transmitted in this way.

Similar events

Another strong solar storm happened in February 1872. Less severe storms occurred in 1921 (similar in some ways), 1938, 1941, 1958, 1959, and 1960, when radio signals were disrupted over large areas. The flares and CMEs from the August 1972 solar storms were similar in size and strength to the Carrington event; however, they did not cause an extreme geomagnetic storm. In March 1989, a geomagnetic storm caused power outages across large parts of Quebec. The 2003 Halloween solar storms were the strongest solar explosions ever recorded. On July 23, 2012, a "Carrington-class" solar superstorm (including a solar flare, CME, and solar electromagnetic pulse) was observed, but its path narrowly missed Earth, with a trajectory that would have hit Earth nine days later. During the May 2024 solar storms, an aurora borealis was seen as far south as Puerto Rico.

In June 2013, researchers from Lloyd's of London and Atmospheric and Environmental Research (AER) in the United States used data from the Carrington Event to estimate the cost of a similar event today in the United States alone at about $600 billion to $2.6 trillion (equivalent to $794 billion to $3.44 trillion in 2024). This cost would be roughly 3.6 to 15.5 percent of the United States’ annual GDP. In addition to economic effects, research suggests that large geomagnetic storms could indirectly harm agriculture by disrupting access to agricultural inputs like fertilizer or pesticides, due to interruptions in industrial production. This could reduce global crop yields by 38–48 percent, with losses as high as 75 percent in some regions, such as Central Europe.

Other studies have examined signs of large solar flares and CMEs in carbon-14 found in tree rings and beryllium-10 in ice cores. Evidence of a large solar storm has been found for the years 774–775 and 993–994. Carbon-14 levels from 775 suggest an event about 20 times stronger than normal solar activity and 10 or more times the size of the Carrington Event. An event in 7176 BCE may have been even stronger than the 774–775 CE event, based on this data.

Scientists are still unsure if the physics of solar flares is the same as that of larger superflares. The Sun may differ in important ways, such as size and rotation speed, from stars known to produce superflares.

Other evidence

Scientists have studied thin layers rich in nitrate found in ice cores to learn about past solar storms that happened before reliable observations were available. This method is based on the idea that high-energy particles from the sun could cause nitrogen in the air to change, creating compounds like nitric oxide. These compounds would not be spread too far in the atmosphere before being trapped in snow and forming layers in ice.

Starting in 1986, some scientists said that data from Greenland ice cores showed signs of individual solar particle events, including the Carrington Event. However, more recent research on ice cores has made scientists question this conclusion. It suggests that spikes in nitrate levels may be caused by events on Earth, such as forest fires, and match other signs linked to smoke from fires. Nitrate levels in ice cores from Greenland and Antarctica do not match, which weakens the idea that these spikes were caused by solar particle events.

A 2024 study examined digital records of magnetic field measurements from observatories in Kew and Greenwich. The results showed that changes in the magnetic field occurred at rates faster than the highest levels ever recorded for that area, based on modern digital data. This indicates that the magnetic field changed much more quickly than previously thought.