Last month, Earth was treated to a massive aurora borealis that reached as far south as Texas. The event was attributed to a solar storm that lasted nearly a full day and will likely contend for the strongest of 2026. Such solar storms are usually fun for people on Earth, as we are protected from solar radiation by our planet’s atmosphere, so we can just enjoy the gorgeous greens and pretty purples in the night sky.

But solar storms are a lot more than just the aurora borealis we see, and sometimes they can cause real damage. There are several examples of this in recorded history, with the earliest being the Carrington Event, a solar storm that took place on Sept. 1, 1859. It remains the strongest solar storm ever recorded, where the world’s telegraph machines became overloaded with energy from it, causing them to shock their operators, send ghost messages and even catch on fire. 

Things have changed a lot since the mid-1800s, and while today’s technology is a lot more resistant to solar radiation than it once was, a solar storm of that magnitude could still cause a lot of damage. 

What is a solar storm?

A solar storm is a catchall term that describes any disturbance in the sun that involves the violent ejection of solar material into space. This can come in the form of coronal mass ejections, where clouds of plasma are ejected from the sun, or solar flares, which are concentrated bursts of electromagnetic radiation (aka light). 

A sizable percentage of solar storms don’t hit Earth, and the sun is always belching material into space, so minor solar storms are quite common. The only ones humans tend to talk about are the bigger ones that do hit the Earth. When this happens, it causes geomagnetic storms, where solar material interacts with the Earth’s magnetic fields, and the excitations can cause issues in everything from the power grid to satellite functionality. It’s not unusual to hear «solar storm» and «geomagnetic storm» used interchangeably, since solar storms cause geomagnetic storms. 

Solar storms ebb and flow on an 11-year cycle known as the solar cycle. NASA scientists announced that the sun was at the peak of its most recent 11-year cycle in 2024, and, as such, solar storms have been more frequent. The sun will metaphorically chill out over time, and fewer solar storms will happen until the cycle repeats. 

This cycle has been stable for hundreds of millions of years and was first observed in the 18th century by astronomer Christian Horrebow.

How strong can a solar storm get?

The Carrington Event is a standout example of just how strong a solar storm can be, and such events are exceedingly rare. A rating system didn’t exist back then, but it would have certainly maxed out on every chart that science has today. 

We currently gauge solar storm strength on four different scales. 

The first rating that a solar storm gets is for the material belched out of the sun. Solar flares are graded using the Solar Flare Classification System, a logarithmic intensity scale that starts with B-class at the lowest end, and then increases to C, M and finally X-class at the strongest. According to NASA, the scale goes up indefinitely and tends to get finicky at higher levels. The strongest solar flare measured was in 2003, and it overloaded the sensors at X17 and was eventually estimated to be an X45-class flare. 

CMEs don’t have a named measuring system, but are monitored by satellites and measured based on the impact they have on the Earth’s geomagnetic field. 

Once the material hits Earth, NOAA uses three other scales to determine how strong the storm was and which systems it may impact. They include: 

• Geomagnetic storm (G1-G5): This scale measures how much of an impact the solar material is having on Earth’s geomagnetic field. Stronger storms can impact the power grid, electronics and voltage systems. 
• Solar radiation storm (S1-S5): This measures the amount of solar radiation present, with stronger storms increasing exposure to astronauts in space and to people in high-flying aircraft. It also describes the storm’s impact on satellite functionality and radio communications. 
• Radio blackouts (R1-R5): Less commonly used but still very important. A higher R-rating means a greater impact on GPS satellites and high-frequency radios, with the worst case being communication and navigation blackouts. 

Solar storms also cause auroras by exciting the molecules in Earth’s atmosphere, which then light up as they «calm down,» per NASA. The strength and reach of the aurora generally correlate with the strength of the storm. G1 storms rarely cause an aurora to reach further south than Canada, while a G5 storm may be visible as far south as Texas and Florida. The next time you see a forecast calling for a big aurora, you can assume a big solar storm is on the way. 

How dangerous is a solar storm?

The overwhelming majority of solar storms are harmless. Science has protections against the effects of solar storms that it did not have back when telegraphs were catching on fire, and most solar storms are small and don’t pose any threat to people on the surface since the Earth’s magnetic field protects us from the worst of it.

That isn’t to say that they pose no threats. Humans may be exposed to ionizing radiation (the bad kind of radiation) if flying at high altitudes, which includes astronauts in space. NOAA says that this can happen with an S2 or higher storm, although location is really important here. Flights that go over the polar caps during solar storms are far more susceptible than your standard trip from Chicago to Houston, and airliners have a whole host of rules to monitor space weather, reroute flights and monitor long-term radiation exposure for flight crews to minimize potential cancer risks.

Larger solar storms can knock quite a few systems out of whack. NASA says that powerful storms can impact satellites, cause radio blackouts, shut down communications, disrupt GPS and cause damaging power fluctuations in the power grid. That means everything from high-frequency radio to cellphone reception could be affected, depending on the severity.

A good example of this is the Halloween solar storms of 2003. A series of powerful solar flares hit Earth on Oct. 28-31, causing a solar storm so massive that loads of things went wrong. Most notably, airplane pilots had to change course and lower their altitudes due to the radiation wreaking havoc on their instruments, and roughly half of the world’s satellites were entirely lost for a few days.

A paper titled Flying Through Uncertainty was published about the Halloween storms and the troubles they caused. Researchers note that 59% of all satellites orbiting Earth at the time suffered some sort of malfunction, like random thrusters going offline and some shutting down entirely. Over half of the Earth’s satellites were lost for days, requiring around-the-clock work from NASA and other space agencies to get everything back online and located.

Earth hasn’t experienced a solar storm on the level of the Carrington Event since it occurred in 1859, so the maximum damage it could cause in modern times is unknown. The European Space Agency has run simulations, and spoiler alert, the results weren’t promising. A solar storm of that caliber has a high chance of causing damage to almost every satellite in orbit, which would cause a lot of problems here on Earth as well. There were also significant risks of electrical blackouts and damage. It would make one heck of an aurora, but you might have to wait to post it on social media until things came back online.

Do we have anything to worry about?

We’ve mentioned two massive solar storms with the Halloween storms and the Carrington Event. Such large storms tend to occur very infrequently. In fact, those two storms took place nearly 150 years apart. Those aren’t the strongest storms yet, though. The very worst that Earth has ever seen were what are known as Miyake events.

Miyake events are times throughout history when massive solar storms were thought to have occurred. These are measured by massive spikes in carbon-14 that were preserved in tree rings. Miyake events are few and far between, but science believes at least 15 such events have occurred over the past 15,000 years. That includes one in 12350 BCE, which may have been twice as large as any other known Miyake event. 

They currently hold the title of the largest solar storms that we know of, and are thought to be caused by superflares and extreme solar events. If one of these happened today, especially one as large as the one in 12350 BCE, it would likely cause widespread, catastrophic damage and potentially threaten human life. 

Those only appear to happen about once every several hundred to a couple thousand years, so it’s exceedingly unlikely that one is coming anytime soon. But solar storms on the level of the Halloween storms and the Carrington Event have happened in modern history, and humans have managed to survive them, so for the time being, there isn’t too much to worry about.