On the night of 10 May 2024, people who had never seen the northern lights watched them ripple over Mexico, Portugal, and Spain. The cause was a barrage of eruptions from a single restless patch of the Sun, which slammed into Earth's magnetic field and produced the strongest geomagnetic storm in two decades — an event forecasters rated G5, the top of NOAA's storm scale, and later named the "Gannon storm" [source: NASA, 2024]. Five months later, on 15 October 2024, NASA, NOAA, and the international Solar Cycle Prediction Panel confirmed what the sky had been hinting at: the Sun had entered solar maximum, the stormy peak of its 11-year cycle [source: NASA, 2024].
That combination — a spectacular light show and an official peak in solar activity — is why space weather is suddenly a mainstream topic. But the auroras are the friendly face of a phenomenon with a harder edge. The same storms that paint the sky can nudge satellites out of orbit, scramble the GPS signals that guide tractors and aircraft, and, in the worst historical cases, knock out power grids. This article separates the show from the stakes: what solar maximum actually is, how a storm travels from the Sun to your sky, what it can and cannot do to the technology we depend on, and how far forecasting has really come.
In this article
- Why the Sun has a stormy season
- From the Sun to your sky — what a geomagnetic storm is
- The light show — and why it reached the tropics
- Beyond the auroras — the real risks
- When it has gone wrong before
- The Carrington worst case — scenario, not certainty
- How forecasting works, and where it stops
- Conclusion — what to watch
Why the Sun has a stormy season
The Sun is not a steady lamp. Its magnetic field winds itself up and unravels on a rhythm of roughly 11 years, a pattern known as the solar cycle. Near the low point, the Sun's face can go weeks without a blemish. Near the high point — solar maximum — its surface is freckled with sunspots, dark regions of concentrated magnetic field, and it flares far more often. At maximum the Sun's magnetic poles actually flip, north trading places with south [source: NASA, 2024]. We are living through that peak now: on 15 October 2024, NASA, NOAA, and the international Solar Cycle Prediction Panel announced that the current cycle, Solar Cycle 25, had reached its maximum phase, expected to last about another year before activity declines [source: NASA, 2024].
Here it helps to separate expectation from measurement. When Solar Cycle 25 began in 2019, the prediction panel forecast a relatively weak-to-average cycle. The Sun did not read the memo: observed sunspot counts have slightly exceeded that forecast, reaching a 23-year high in August 2024, and on 3 October 2024 the cycle produced its strongest flare so far, an X9.0 [source: NASA, 2024]. This gap between a cautious prediction and a livelier reality is worth holding onto, because it runs through the whole subject — the Sun is forecastable in broad strokes and stubbornly surprising in the details.
One caution about the word "maximum" itself: the exact peak month cannot be pinned down in real time. Scientists can only identify it in hindsight, months or years later, once they see a sustained decline [source: NASA, 2024]. So "we are at solar maximum" is a statement about a period, not a single day.
From the Sun to your sky — what a geomagnetic storm is
A geomagnetic storm is not the sunlight you feel on your face; it is a disturbance in Earth's magnetic environment driven by material and magnetism thrown off by the Sun. Three different things often get blurred together. A solar flare is a flash of light and X-rays; it crosses the 150-million-kilometre gap in about eight minutes and can black out high-frequency radio on Earth's daylit side almost immediately. A coronal mass ejection (CME) is heavier and slower: a cloud of billions of tonnes of magnetized plasma that takes roughly one to three days to reach us. And the steady solar wind blows past all the time. It is mainly the CMEs, and the magnetic field they carry, that drive the biggest storms [source: NOAA NESDIS, 2024].
When that magnetized cloud arrives, it squeezes and stretches Earth's magnetosphere — the protective magnetic bubble around the planet. Charged particles are funnelled down toward the magnetic poles, where they excite gases in the upper atmosphere and make them glow: the aurora. At the same time, the rapidly changing magnetic field acts like a giant, invisible dynamo, inducing electric currents in the ground and in anything long and conductive — pipelines, railway lines, and above all high-voltage power lines. That last effect, not the pretty lights, is where the risk lives.
To turn this into something forecasters can communicate, NOAA uses a set of plain-numbered scales. Geomagnetic storms run from G1 (minor) to G5 (extreme); separate scales track solar-radiation storms (S1–S5) and radio blackouts (R1–R5) [source: NOAA SWPC, 2024]. The May 2024 event hit G5. It is a useful shorthand, but keep the distinction between perception and measurement in mind: a brilliant aurora is what you see, while G5 is a measured statement about how hard the planet's magnetic field was shaken.
The light show — and why it reached the tropics
Auroras are normally a high-latitude privilege, seen from places like northern Canada, Scandinavia, or Antarctica. What made May 2024 remarkable was how far south the glow reached — observers reported it from Mexico, Portugal, and Spain [source: NASA, 2024]. The reason is straightforward: the stronger the storm, the more Earth's magnetic field is compressed and the further from the poles the auroral oval expands. A G5 storm pushes that boundary toward the equator, so regions that never see auroras suddenly do.
History offers an even more extreme version. During the great storm of 1859 — the Carrington Event, discussed below — auroras were reported as far south as Panama and the Caribbean, bright enough that some people rose in the middle of the night thinking it was dawn [source: NOAA NESDIS, 2024]. That is a useful reference point for scale, but also a place to keep perception and data apart. Nineteenth-century aurora sightings are eyewitness reports, vivid but qualitative; modern claims that a given storm was "the biggest in decades" rest on instrument records of the magnetic field, not on how impressive the sky looked. Both matter, but they are different kinds of evidence, and the honest way to describe a storm is with the measured numbers, not the gasps.
Beyond the auroras — the real risks
Once a storm is strong enough to light up the tropics, it is also strong enough to reach the technologies threaded through modern life. Four systems are worth understanding, because the risks are concrete and, in most cases, already documented.
Satellites and low-Earth orbit
A geomagnetic storm heats and puffs up the upper atmosphere, so the thin gas at satellite altitudes becomes denser and drags harder on anything flying through it. In February 2022 this caught SpaceX off guard: a day after launching 49 Starlink satellites into a low orbit, a moderate storm increased atmospheric drag by up to about 50%, and 38 of the 49 satellites could not climb to their operating altitude and re-entered the atmosphere [source: Space Weather (AGU), 2022]. This is a case where correlation and cause must be handled carefully — the space weather was not extreme; it combined with a deliberately low insertion altitude and the satellites' light build to produce the loss. As Solar Cycle 25 stays active, researchers expect such drag events in low orbit to become more frequent [source: Space Weather (AGU), 2022].
Navigation and GPS
Storms disturb the ionosphere, the electrically charged layer that satellite-navigation signals pass through, degrading position accuracy. During the May 2024 storm, a Boston University team using about 100 high-accuracy fixed GPS receivers across the United States measured position errors of up to roughly 70 metres [source: Boston University, 2025]. The practical bite landed on agriculture: the storm struck during peak spring planting, when GPS-guided tractors that normally steer to centimetre accuracy were pulled from fields because their guidance had drifted. One economic analysis estimated the disruption cost US grain producers on the order of US$500 million — a figure best read as an estimate, not a settled loss [source: Boston University, 2025].
Aviation
Flights over the poles rely on high-frequency radio and can be exposed to elevated radiation during solar storms. The 2003 Halloween storms offer the clearest documented example: after a major flare, high-frequency radio was impaired for more than two hours, and several polar flights had to reroute to lower-latitude paths, burning extra fuel and cutting cargo; the US Federal Aviation Administration issued a radiation alert and airlines lowered altitudes and changed routes to limit crew and passenger dose [source: Space Weather (AGU), 2023].
Power grids
The most serious risk is to electricity networks. The geomagnetically induced currents that a storm drives through long transmission lines can push large transformers into overheating and, in extreme cases, permanent damage. These are the failures that turn a sky-watching event into an infrastructure event — and, as the next section shows, they are not hypothetical.
When it has gone wrong before
Two events anchor the historical record, and both are verified rather than modelled. On 13 March 1989, a CME struck Earth and, about 90 seconds later, the Hydro-Québec grid in Canada collapsed. Geomagnetically induced currents tripped five transmission lines from the James Bay complex, dropping about 9,450 megawatts of generation; the system could not absorb the sudden loss and failed within seconds, leaving roughly six million people without power for about nine hours [source: Hydro-Québec, 2024]. It remains the archetypal space-weather blackout, and Hydro-Québec has since spent heavily on protections.
The Halloween storms of October 2003 were milder in their grid impact but wider in reach. In Malmö, Sweden, around 50,000 people briefly lost power, and in South Africa a large power-station transformer suffered magnetic-current stress that contributed to its failure weeks later [source: Space Weather (AGU), 2023]. Together, 1989 and 2003 establish an important, sober point: the grid damage from space weather is real and has happened, but the observed events so far have been regional and recoverable, not civilizational. That distinction matters when we turn to the worst-case scenarios, which are a different kind of claim.
The Carrington worst case — scenario, not certainty
The reference point for "how bad could it get" is the Carrington Event of September 1859, when the astronomer Richard Carrington watched a brilliant flash erupt from a sunspot group. It is the most intense space-weather event on record. With little electrical infrastructure to damage, its main victim was the telegraph network: operators were shocked, equipment sparked, and on some lines the current was so strong that messages could be sent with the batteries disconnected, the storm itself powering the wires [source: NOAA NESDIS, 2024]. The obvious question is what a storm of that size would do to a civilization now wired end to end.
This is where care is essential, because the eye-catching numbers are modelled scenarios, not measurements or forecasts. A 2008 workshop report from the US National Academies of Sciences estimated that a severe geomagnetic-storm scenario could cost US$1–2 trillion in its first year, with full recovery taking four to ten years, driven largely by damage to hard-to-replace high-voltage transformers [source: National Academies of Sciences, 2008]. A 2013 risk study commissioned by the insurance market Lloyd's put 20–40 million people in North America at risk of outages lasting anywhere from 16 days to one or two years, again hinging on transformer replacement times [source: Lloyd's, 2013]. NOAA notes that Carrington-scale events may occur roughly once every 500 years, with smaller storms far more often — though that recurrence figure is itself uncertain [source: NOAA NESDIS, 2024].
These estimates deserve to be taken seriously as planning tools, and equally deserve to be labelled honestly. They are projections built on assumptions about how grids, transformers, and supply chains would behave under stress the modern system has never actually faced; experts genuinely disagree about how severe the real damage would be. The gap between "a plausible worst case" and "what will happen" is wide, and closing it is exactly what forecasting and grid engineering are trying to do.
How forecasting works, and where it stops
Space-weather forecasting looks a little like weather forecasting, with one hard constraint: the most decisive information often arrives only minutes before the storm does. In the United States, NOAA's Space Weather Prediction Center issues the official watches and warnings. Its most time-critical data come from spacecraft parked at L1, a gravitational balance point about 1.5 million kilometres sunward of Earth, where the aging DSCOVR (NOAA, launched 2015), ACE (NASA, 1997), and SOHO (NASA–ESA, 1995) sample the solar wind before it reaches us [source: NOAA NESDIS, 2024]. The catch is geometry: because L1 sits so close to Earth on cosmic scales, it provides only about 15 to 60 minutes of warning about the magnetic orientation of an incoming CME — the single factor that most determines how damaging a storm will be.
Two newer missions aim to widen that window. NOAA's SWFO-L1 — launched in September 2025 and renamed SOLAR-1 after reaching L1 in January 2026 — carries a compact coronagraph and particle sensors dedicated to spotting and tracking Earth-bound CMEs, replacing instruments that are long past their design lives [source: NOAA, 2025]. And the European Space Agency's Vigil mission, planned for launch around 2031, will take up station at L5, off to the side of the Sun–Earth line, where it can watch active regions and CMEs from an angle days before they rotate to face Earth [source: ESA, 2024]. Better vantage points mean earlier, more confident alerts.
But forecasting has a floor it cannot dig below. A CME's geo-effectiveness depends on the orientation of the magnetic field buried inside it, and that is usually knowable with confidence only when the cloud sweeps past L1 — leaving grid operators and satellite controllers with minutes, not days, to act on the specifics. Longer-range forecasts can say a storm is likely; the fine print that decides whether transformers are truly at risk tends to arrive last. That is not a failure of the science so much as the physics of the problem, and it is why hardening the grid matters as much as watching the Sun.
Conclusion — what to watch
Pull the threads together and the honest summary is this. The Sun is at the peak of an unexpectedly lively cycle; the May 2024 auroras were the visible sign of a genuinely strong storm; and beneath the light show sits a real but bounded set of risks to satellites, navigation, aviation, and power grids. The failures we have actually observed — Québec in 1989, the Halloween storms of 2003, the Starlink losses of 2022 — have been serious but regional and recoverable. The trillion-dollar, multi-year scenarios are worth planning against, but they are modelled projections, not predictions, and reasonable experts disagree about them.
What should you watch from here? First, whether the tail of Solar Cycle 25 delivers more strong storms as the peak persists into its decline. Second, whether the new eyes on the Sun — SOLAR-1 at L1, Vigil at L5 — meaningfully lengthen warning times over the next several years. And third, the quieter, more consequential story: how far grid operators and satellite builders go in hardening their systems, since the surest protection against space weather is not a better view of the storm but infrastructure that can ride it out. The auroras will keep coming back. The question is whether we treat them as a spectacle or as a warning.
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