What Is Solar Maximum? | Extremetech

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NASA recently announced that as of late October, the Sun has reached solar maximum: a repeating crescendo of solar activity that often comes with increased solar flares. True to form, it seems like there’s another flare every few days. Rapid-fire solar flares have been lighting up the night skies with the aurora, as far south as Florida and Puerto Rico, since last year. Solar max is projected to last well into the second half of 2025. So what’s going on here? Is it any danger to us? To understand solar maximum, let’s start with the solar cycle.

The solar cycle is the natural cycle of the Sun as it transitions between periods of low and high activity. (Currently, we’re in solar cycle 25: the 25th observed solar cycle since scientists started recording them.) Roughly every 11 years, at the peak of the solar cycle, the Sun’s magnetic poles flip—on Earth, that would be like the North and South Poles swapping places every decade—and the Sun transitions from sluggish to spicy.

Fossil records suggest that the 11-year solar cycle has been stable for at least the last 700 million years.

Sunspots

Chronologically, solar weather starts with sunspots. The Sun’s changing magnetic field can create turbulence in the Sun’s outermost layers. These irregularities create zones of high magnetic strain within the plasma surface layer. Eventually, the strain is just too much, and like an electrical arc, the strain equalizes itself. All that potential energy is suddenly released, and more often than not, there’s a burst of plasma that blasts out of the Sun like a tongue of flame.

Credit: NASA

“During solar maximum, the number of sunspots, and therefore, the amount of solar activity, increases,” said Jamie Favors, director of the Space Weather Program at NASA Headquarters in Washington. “This increase in activity provides an exciting opportunity to learn about our closest star—but also causes real effects at Earth and throughout our solar system.”

Credit: NASA

Solar flares and coronal mass ejections are the two forms of solar weather most impactful to life on Earth.

“Solar Cycle 25 sunspot activity has slightly exceeded expectations,” said Lisa Upton, co-chair of the Solar Cycle Prediction Panel and lead scientist at Southwest Research Institute in San Antonio, Texas. “However, despite seeing a few large storms, they aren’t larger than what we might expect during the maximum phase of the cycle.”

How Does the Solar Cycle Affect Earth?

Solar activity strongly influences conditions in space, known as space weather. This can affect satellites and astronauts in space, as well as communications and navigation systems—such as radio and GPS—and power grids on Earth. Near solar maximum, frequent solar flares blast away some of the cosmic rays that would otherwise hit Earth. Evidence for solar flares comes from ice cores, and the growth rings of trees.

Credit: NASA

Most of the time, solar weather only noticeable at ground level via the aurora, with just a few events that impact Earth. Earth’s atmosphere and magnetosphere protect us from the high-intensity radiation of solar flares and the massive jet of plasma from CMEs. The atmosphere prevents high-energy particles from reaching the ground, and it’s denser near ground level, so the protection is strongest where people spend their time. Meanwhile, our planet’s magnetosphere deflects the electromagnetic radiation, routing it poleward along Earth’s magnetic field lines.

Most of the time, that’s enough. But near solar max, it’s a different story—and every so often, Earth loses the sunspot lottery.

Fire in the Skies

For extreme solar weather, our high-water mark is often the Carrington Event of 1859: a powerful solar storm named after Richard Carrington, an English astronomer who saw the flare that caused it with his own two eyes.

During the event, the aurora borealis was so bright that it woke up a Colorado mining camp in the middle of the night; their cooks started to brew coffee, thinking the sun was rising. Folks in New York City reported being able to read the newspaper by the light of the aurora. But ground-level geomagnetic disturbances were strong enough that things got really weird. Two operators of the telegraph line between Boston, Massachusetts, and Portland, Maine, exchanged this conversation on the night of Sept. 2, 1859 (as reported by the Boston Evening Traveler):

Boston operator (to Portland operator): “Please cut off your battery [power source] entirely for fifteen minutes.”

Portland operator: “Will do so. It is now disconnected.”

Boston: “Mine is disconnected, and we are working with the auroral current. How do you receive my writing?”

Portland: “Better than with our batteries on. – Current comes and goes gradually.”

Boston: “My current is very strong at times, and we can work better without the batteries, as the aurora seems to neutralize and augment our batteries alternately, making current too strong at times for our relay magnets. Suppose we work without batteries while we are affected by this trouble.”

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

Boston: “Yes. Go ahead.”

The conversation carried on via unplugged equipment for two hours. Less whimsically, telegraph operators elsewhere reported showers of sparks coming from their equipment—some setting fires. (Imagine a Star Trek bridge console when the Enterprise gets hit.)

Low Probability, High Risk

Storms like these aren’t common, but neither are they vanishingly rare; they’re enough of a hazard that actuaries and government agencies both pay attention to the risk. They’re more likely near solar maximum, when solar weather is at its peak intensity.

Over the long arc of history, there have been dozens of CMEs that scored a direct hit on Earth. Just within the past couple decades, Earth has had several “Carrington-class” near misses. The 2003 Halloween solar storms produced the most powerful solar explosions ever recorded. We don’t actually know how powerful the largest was, because it totally saturated the detector array on our GOES satellites, but they top out at X28; heliophysicists have since revised their estimate sharply upward, to an X45. (Yikes.) There was a near miss in July 2012, and another in May of 2024, during which the aurora was visible as far south as Puerto Rico.

The face of the Sun on May 6, 2024, with two sunspot clusters (top right: AR 3663, bottom left: AR 3664) that triggered a series of X-class solar flares, compared to the Carrington Event sunspots (superimposed, center).
Credit: SDO/HMI

Satellite “megaconstellations,” like Starlink and China’s upcoming Thousand Sails, are exquisitely sensitive to space weather. During the rapid-fire burst of solar flares this past May, not only did Earth experience several short-wave radio and GPS blackouts due to EM interference, but the satellites themselves were in danger. When a CME hits Earth, our atmosphere absorbs so much energy that it puffs up like a marshmallow in the oven. Thousands of Starlink satellites had to abruptly change altitude to deal with atmospheric friction.

So, should you take action to protect against inclement solar weather? In a word: meh. Maybe unplug electronics you don’t want to get zapped. Most of the headaches caused by solar flares seem to fall on the folks who maintain infrastructure.

Satellite disruptions and interference are problems, true enough. For instance, buying gas with debit or credit is a satellite transaction. And it’s important to keep your important data backed up in case of a power surge, although electronic backups may do little good. A solar storm in 1989 halted all trading at the Toronto stock exchange when a power surge fried three redundant hard drives. An earlier storm in 1979 even resulted in dozens of magnetically triggered sea mines exploding all at once, out of nowhere.

But that shrinks to an inconvenience compared with possible issues in the power grid. Power surges caused by inclement space weather could blow out the massive transformers between power plants and the grid. “Transformers can take a long time to replace, especially if hundreds are destroyed at once,” said Daniel Baker, of the University of Colorado’s Laboratory for Atmospheric and Space Physics. (Baker coauthored a National Research Council report on solar-storm risks.)

Taken from the International Space Station by astronaut Jasmin Moghbeli during a solar storm in October 2024.
Credit: Jasmin Moghbeli/X

“Imagine large cities without power for a week, a month, or a year,” Baker said. “The losses could be $1 to $2 trillion, and the effects could be felt for years.”

Experts agree that the eastern half of North America is especially vulnerable, with its metropolitan sprawl from Atlanta to Toronto, because the power infrastructure is highly interconnected. Failures can easily cascade. It’s happened before; that 1989 solar storm knocked out power to most of Quebec within 90 seconds, and the disruption caused downstream grid “anomalies” throughout the Northeast and Mid-Atlantic. In August 2003, a few months before the Halloween storms, foliage on Canadian power lines caused what should have been a local blackout to escalate into a 3.5-gigawatt power surge that knocked out power to most of the Northeast. And in 2019, a single storm knocked out power to more than three million people in a swathe across Quebec, Ontario, and fourteen US states.

Happily, we do get some warning when dangerous solar weather strikes.

Solar Fields

Scientists use telescopes and magnetometers to study many aspects of the Sun, including space weather, the solar dynamo, solar cycles, and the internal fusion by which the Sun produces light—all of which fall under the aegis of heliophysics.

It is possible, but difficult, to make telescope observations of the Sun from Earth’s surface. Much of the Sun’s activity is best visible in ultraviolet wavelengths. However, our atmosphere absorbs the vast majority of the UV radiation that would otherwise hit the surface. Several government agencies (mostly NASA and NOAA) have solar observatory satellites.

Credit: NASA

Out of the fleet, the best known may be the GOES solar satellites, which power NASA’s Solar Dynamics Observatory. In September, NOAA fired up the latest: GOES-19.