The Carrington Event was the strongest magnetic storm ever recorded, reaching its peak on September 1–2, 1859, during solar cycle 10. It caused bright lights in the sky, seen around the world, and led to sparks and fires at telegraph stations. This storm was likely caused by a burst of energy from the Sun, called a coronal mass ejection, hitting Earth's magnetic field.

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

History

On September 1 and 2, 1859, one of the largest geomagnetic storms (as measured by ground-based magnetometers) occurred. Scientists estimate the storm's strength (measured as Dst) was between −0.80 and −1.75 μT.

This storm is believed to have been caused by a coronal mass ejection (CME) that traveled directly toward Earth. The CME took 17.6 hours to cover a distance of 150 × 10⁶ km (93 × 10⁶ mi). Most CMEs take several days to reach Earth, but this one moved quickly. Scientists think a previous CME, possibly linked to a large aurora event on August 29, may have cleared the path of solar wind plasma, allowing this CME to travel faster.

On September 1, 1859, just before noon, English astronomers Richard Carrington and Richard Hodgson independently observed and recorded the earliest known solar flare. They shared their findings in separate reports published in Monthly Notices of the Royal Astronomical Society. Their drawings of the event were displayed at the November 1859 meeting of the Royal Astronomical Society.

Scottish physicist Balfour Stewart noticed a geomagnetic solar flare effect, called a "magnetic crochet," in magnetometer records from the Kew Observatory. He also observed a geomagnetic storm the next day. These events led Carrington to suspect a connection between the Sun and Earth, though he was unsure if the two were related. He wrote, "one swallow does not make a summer." American mathematician Elias Loomis later compiled worldwide reports of the 1859 geomagnetic storm, supporting Carrington’s and Stewart’s observations.

Impact

Auroras were seen in both the northern and southern parts of the world. In the United States, the aurora borealis over the Rocky Mountains was so bright that it woke up gold miners, who thought it was morning and began to make breakfast. People in the northeastern United States could read a newspaper by the light of the aurora. The aurora was also visible from the poles to areas near the equator, such as 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 outside late on Thursday night saw a beautiful display of auroral lights. The lights were similar to a display seen earlier, but at times they were even brighter, and the colors were more varied and striking. The lights filled the sky, appearing like a glowing cloud through which stars shone faintly. The brightness was greater than that of a full moon, but the light felt soft and gentle. Between 12 and 1 a.m., when the display was brightest, the quiet city streets looked both beautiful and unusual under this strange light.

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

I was digging for gold at Rokewood, about four miles from Rokewood township in Victoria. Myself and two friends saw a bright reflection in the southern sky around 7 p.m. Within half an hour, a scene of amazing beauty appeared. Lights of every color came from the southern sky, with one color fading to make way for another, sometimes more beautiful than the last. The lights rose toward the top of the sky, turning a rich purple at the highest point, and curled around, leaving a clear space in the sky. The northern part of the sky also had beautiful colors, which were thought to be a copy of the southern display because the colors matched. This was a sight people would never forget, and it was considered the most powerful aurora ever recorded. Some people saw it as a sign of divine presence, while others felt it was a warning of something bad to come.

Because of the electrical current caused by the aurora’s electromagnetic field, telegraph systems in Europe and North America stopped working. In some cases, operators received electric shocks. Telegraph towers sparked. Some operators could still send and receive messages even after turning off their power supplies. On the night of September 2, 1859, two telegraph operators in the United States had the following conversation, 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 slowly."

Boston: "My current is very strong at times, and we can work better without batteries because 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 lasted about two hours, using only the current from the aurora and no battery power. This was the first time in history that more than a few words were sent in this way.

Similar events

Another strong solar storm happened in February 1872. Less severe storms occurred in 1921, 1938, 1941, 1958, 1959, and 1960. Some of these were similar to the 1872 storm. During these years, radio disruptions were reported in many places. The solar flares and coronal mass ejections (CMEs) in August 1972 were as large as those during the Carrington event in 1859. However, the 1972 storms did not cause a very strong magnetic storm. In March 1989, a magnetic storm caused power outages in much of Quebec. In 2003, the Halloween solar storms were the strongest solar explosions ever recorded. On July 23, 2012, a solar superstorm similar to the Carrington event was observed. However, it did not hit Earth because its path missed Earth by about nine days. During the May 2024 solar storms, the northern lights were 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 information from the Carrington Event to estimate the cost of a similar event today. They calculated that such an event could cost the United States alone between $600 billion and $2.6 trillion (equivalent to about $794 billion to $3.44 trillion in 2024). This would be about 3.6 to 15.5 percent of the country's yearly economic output. In addition, studies suggest that a large magnetic storm could harm agriculture. This would happen indirectly, by disrupting the production of items like fertilizer or pesticides. These disruptions could reduce global crop yields by 38–48 percent, with some areas, like Central Europe, losing up to 75 percent of their crops.

Other research has studied evidence of large solar flares and CMEs in tree rings and ice cores. Scientists have found signs of major solar storms in the years 774–775 and 993–994. Carbon-14 levels in tree rings from 775 suggest an event about 20 times stronger than normal solar activity, and 10 or more times the size of the Carrington Event. Evidence also suggests that an event in 7176 BCE may have been even larger than the 774–775 CE event.

It is still unclear whether solar flares on the Sun are similar to superflares on other stars. The Sun may differ in size and how fast it rotates compared to stars that produce superflares.

Other evidence

Scientists have studied thin layers in ice cores that contain high levels of nitrate to learn about past solar storms that happened before modern observations began. This method relies on the idea that particles from the sun could change the charge of nitrogen in the air, creating nitrogen compounds like nitric oxide. These compounds would not mix too much with the atmosphere before being trapped in snow and forming layers in ice.

Starting in 1986, some scientists said that ice cores from Greenland showed signs of specific solar events, including the Carrington Event. However, more recent research on ice cores suggests that sharp increases in nitrate levels may not be caused by solar particles but instead by events on Earth, such as forest fires. These nitrate spikes match other chemical signs found in smoke from known forest fires. Nitrate levels in ice cores from Greenland and Antarctica do not match, which makes it unlikely that these layers reflect solar proton events.

A 2024 study examined digital records of magnetic field measurements from observatories in Kew and Greenwich. The analysis showed that changes in the magnetic field occurred at rates over 700 nT/min, which is much faster than the typical extreme value of 350–400 nT/min recorded for this region in modern digital data. This suggests the magnetic field changed more quickly than previously thought.