On September 1, 1859, British astronomer Richard Carrington was sketching a large group of sunspots when two patches of white light appeared within them. He watched them brighten, fade and disappear in about five minutes.

Roughly 17 hours later, Earth’s magnetic field convulsed. Auroras spread into the tropics. Telegraph networks misbehaved across Europe and North America. Sparks leaped from equipment, paper reportedly caught fire and some operators received electric shocks.

The episode now called the Carrington Event remains the benchmark for an extreme geomagnetic storm. A repeat would meet a world far more dependent on electricity and signals from space, but it would not work like an electromagnetic switch that instantly kills every phone, car and computer.

Carrington saw the Sun brighten in visible light

Carrington was observing a projected image of the Sun, a method that allowed him to map sunspots without looking through the telescope directly. Another English observer, Richard Hodgson, independently saw the same flash.

Carrington’s original report in the Monthly Notices of the Royal Astronomical Society described two patches of “intensely bright and white light.” It was the first detailed observation of what scientists now call a white-light solar flare.

A flare is a burst of electromagnetic radiation. The geomagnetic storm that followed was driven by magnetized material expelled from the Sun, now understood as a coronal mass ejection, or CME. Light from a flare reaches Earth in about eight minutes. A CME is matter and travels much more slowly, though the 1859 arrival appears to have been exceptionally fast.

The telegraph network became an accidental detector

Telegraph lines were among the longest electrical conductors then in existence. As Earth’s magnetic field changed rapidly, it generated electric fields in the ground. Those fields drove unwanted currents through grounded wires.

The effects varied by line and location. Some systems stopped working. Others produced sparks, shocked operators or became so strongly energized that their normal batteries interfered with communication.

A remarkable set of observations was collected soon afterward in the American Journal of Science. Operators on a line between Boston and Portland disconnected their batteries and continued sending messages using the current induced by the aurora. The current rose and fell on its own, at times becoming too strong for their relay magnets.

The famous shocks are therefore not a later invention. They are consistent with contemporary reports and with the same induction physics that concerns power-grid engineers today.

Auroras reached Cuba and Hawaii

Auroras normally cluster around high geomagnetic latitudes, where charged particles guided by Earth’s magnetic field collide with gases in the upper atmosphere. An intense storm expands the auroral zones toward the equator.

During the 1859 event, observers reported auroras from places that rarely see them. The US National Weather Service records sightings as far south as Cuba and Hawaii. Newspapers described red skies and light bright enough in some locations to read by.

The geographic reach matters more scientifically than the color of any individual report. Low-latitude auroras show how deeply the storm disturbed the magnetosphere, although reconstructing its exact strength from 19th-century instruments and eyewitness accounts leaves substantial uncertainty.

A modern grid has its own version of the telegraph problem

A geomagnetic storm does not need to strike a transformer like lightning. It changes the magnetic field over a large region. The resulting geoelectric field can drive current through long transmission lines and into grounded transformer windings.

Those geomagnetically induced currents can distort transformer operation, create excess heating, confuse protective equipment and make voltage harder to control. Failures in one part of an interconnected network can place extra stress on another.

On NOAA’s G1-to-G5 geomagnetic storm scale, a G5 event can produce widespread voltage-control and protection problems. Some grid systems may experience blackouts, and transformers may be damaged. “May” is important: the outcome depends on storm duration and orientation, grid design, operating decisions and the electrical conductivity of the ground beneath each region.

A 2025 US Geological Survey study modeled a Carrington-class storm across the United States. It found especially strong likely geoelectric fields in parts of the East and Midwest, while values could differ sharply even within one state because underground geology changes how currents flow.

Satellites, navigation and radio would face different hazards

Spacecraft do not experience the ground currents that threaten long power lines. They face charged particles, surface charging, radiation effects and an upper atmosphere heated and expanded by the storm.

NOAA says an extreme geomagnetic storm can cause problems with satellite orientation, tracking, uplinks and downlinks. Increased atmospheric drag can alter the orbits of low-Earth satellites. Operators may need to change spacecraft modes or correct those orbits afterward.

The disturbed ionosphere can also degrade satellite navigation for days and make high-frequency radio communication impossible in many areas for one or two days. Aviation, maritime operations, surveying and precision agriculture can all depend on those services, though backup systems and operating procedures differ by industry.

This is why “the internet would disappear” is too simple. Fiber-optic cable itself does not conduct geomagnetically induced current, but networks depend on powered ground equipment, data centers, timing, satellites and functioning grids. Disruption would arrive through connected infrastructure rather than every piece of electronics being directly fried.

We have warning systems that 1859 did not

Solar observatories can detect an Earth-directed CME and give broad warning measured in hours to days. Spacecraft upstream of Earth then sample the solar wind shortly before it reaches the magnetosphere, refining forecasts of how strongly it may couple with Earth’s field.

That does not make prediction perfect. A NOAA space-weather fact sheet notes that the crucial magnetic orientation of the arriving plasma may only be measured about 15 to 45 minutes before impact. Utilities and satellite operators nevertheless have time to staff control rooms, adjust grid configurations, postpone risky maneuvers and place spacecraft into safer modes.

The G5 storm of May 2024 demonstrated both modern vulnerability and resilience. It disrupted GPS-dependent operations and increased satellite drag, yet it did not produce the universal technological collapse sometimes imagined in Carrington stories.

The exact consequences of another 1859-scale event cannot be reduced to a single damage figure. They would depend on where the strongest magnetic changes occurred, how long they lasted and what operators did in response. The lesson of 1859 is not that civilization would inevitably switch off. It is that long electrical networks can turn a disturbance in near-Earth space into a problem at ground level, and preparation changes the outcome.