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A year ago this weekend, the sun’s activity created some of the most spectacular auroras on record, with displays visible as far south as Florida.

The incredible spectacles last May (and another auroral outburst last October) were partly a matter of luck because several factors, some of them serendipitous, affect the appearance of aurora. But the sun had been primed to put on a show as it approached the maximum phase of its 11-year activity cycle—and that high activity continues today. This solar cycle still has the potential to cause more celestial spectacles before activity calms down. And scientists say that the coming solar cycles may be even more eventful. But it remains quite difficult to predict the sun’s behavior.

“Solar storms—it’s a probabilistic thing, so sometimes they don’t always do what you would expect,” says Lisa Upton, a heliophysicist at the Southwest Research Institute.

The Sun Right Now

The sun is essentially a massive liquid magnet. Heliophysicists gauge our star’s activity by tallying the number of sunspots—relatively “cold” knots of its magnetic field that are often the source of radiation and plasma outbursts—on its surface. (Scientists monitor this tally in real time, but they evaluate the solar cycle’s stages based on smoothed averages over many months. So the formal declaration of a cycle’s solar maximum and minimum always happens after the fact.)

The number of sunspots naturally rises and falls over about 11 years, during which the sun’s magnetic poles first strengthen, then weaken and finally flip. When the sun’s magnetic field is calmest, with one pole that is firmly positive and one that is firmly negative, activity is at its minimum, as it was most recently around December 2019, and the star is sometimes entirely free of blemishes.

For more than a year now, the sun has been in the opposite phase—the solar maximum—with a messy magnetic field, plenty of sunspots and regular outbursts. August 2024 produced the most sunspots of any recent month, with more than 200 such storms.

Sunspots have since become less numerous, but it’s still unclear whether the solar maximum is truly on its way out. “We’ve had a little bit of a slowdown in activity [during] the last couple months. That’s not too surprising,” Upton says. “A question at this point, which will be interesting, is whether or not we’re going to have another little spike in activity.”

She says that if such a spike were to happen, it would likely come within about three months, mirroring a small spike that occurred in June and July 2023. “But the sun likes to surprise us,” Upton adds, “so we’ll see if that happens.”

Long-Term Cycles

Even as scientists watch the current solar cycle unfold, they’re also working to understand what future cycles might bring.

That’s a difficult task, given that modern science is only in the 25th activity cycle, in which researchers have made plentiful sunspot observations. More sophisticated observations that help scientists understand the sun in detail, such as space-based observations and magnetic data, are even newer, with some offering insight into only a couple of solar cycles thus far. Scientists can study tree rings and ice cores to get a basic sense of solar activity before observations began, but these data are less detailed and don’t provide precise sunspot counts.

One hypothesis suggests that the sun displays a longer-term variability called the Gleissberg cycle, named for astronomer Wolfgang Gleissberg, who posited such 80-year cycles in the 1960s. (Other proposed longer-duration cycles in solar behavior include the Suess–de Vries cycle, lasting 195 to 235 years, and the Hallstatt cycle, stretching over some 2,400 years.) And a new analysis of protons trapped in the inner radiation belt that surrounds Earth suggests a new Gleissberg cycle may be beginning.

Not all heliophysicists are sold on the Gleissberg cycle, however, given the scant data scientists have to work with. “It’s kind of debatable whether or not this is a physical phenomenon versus a statistical phenomenon,” Upton says.

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