The sun’s 2024 resolution came in: Let’s get moving.

Solar flares, eruptions on the sun’s surface and sunspots are expected to multiply and intensify throughout this year, as our yellow star enters its most active period in two decades. For Earthlings, that could lead to more beautiful dancing aurora far and wide, but also radio blackouts and satellite disruptions.

“The level of activity here is the biggest it’s been since about 20 years, since about 2003,” said Mark Miesch, a member of the solar modeling team at NOAA’s Space Weather Prediction Center.

If the sun replicates its 2003 behavior, Earth could be in for a treat but also some issues. The Halloween Storms of 2003 brought dazzling green, red and purple aurora all the way to California, Texas, Florida and even Australia. They also disrupted more than half of all spacecraft orbiting Earth, damaged a satellite beyond repair and created communication issues for airlines and research groups in Antarctica.

A suddenly bustling sun may sound worrying, but the sun’s magnetic activity naturally ebbs and flows in 11-year periods, known as the solar cycle. Almost halfway through its current solar cycle, the sun is expected to reach its peak activity between January and October 2024, but activity will probably still be high into 2025 or maybe 2026, according to Space Weather Prediction Center models.

And the upcoming peak should be a decent showing compared with recent cycles. The ramp-up to this “solar maximum” is already stronger than scientists thought, sending impressive punches of solar energy and particles to Earth in 2023 that brought rare aurora sightings to Arizona. It’s already produced more striking solar flares and eruptions than the last solar maximum in 2014.

Even so, scientists predict peak activity will probably be below or about average intensity compared with the long-term average — but it will still be exciting.

“We’ll see some fun stuff in the coming year or couple of years,” said Scott McIntosh, a solar physicist at the National Center for Atmospheric Research in Boulder, Colo. “We’re probably going to get fireworks, whether they’ll be equivalent to Halloween [2003], I don’t know. We should be prepared.”

How do we know when the sun hits peak activity?

Solar maximum becomes obvious once it’s passed, and activity starts to dwindle. But observations of past solar cycles help scientists understand what to quantitively look for ahead of time.

One way to track the waxing and waning activity is by counting the number of temporary dark blotches on the sun’s surface, called sunspots. Sunspots make up “active regions” on the sun, often the source of large explosive bursts of energy known as solar storms. More sunspots generally spell more solar activity.

“Sunspots are connected with magnetic activity on the sun,” said Miesch, also a researcher at University of Colorado at Boulder. Specifically, he said they are locations where magnetic fields are passing from the interior of the sun (where they are generated) through the surface and into the atmosphere.

“We’ve known for about 150 years that the number of spots, if you look on the surface of the sun, it waxes and wanes on a period of about 11 years,” said Miesch. During this 11-year period, the sun’s north and south poles switch places to flip its magnetic field.

The beginning of the 11-year solar cycle has the lowest sunspot number and magnetic activity, known as the solar minimum. Activity ramps up in the middle of the cycle, known as the solar maximum, and eventually decreases back to the minimum.

The sun is currently in its 25th solar cycle since observations in the 1700s.

Across the past 24 solar cycles, the average sunspot number at solar maximum was about 179 sunspots in the peak month, said Miesch. (The last solar maximum in April 2014 peaked only about only 114 sunspots, with that solar cycle the weakest in a century.)

The current solar maximum is predicted to have between 135 to 174 at its greatest month, which is slightly below average, said Miesch, who helped model the current solar cycle and its progression.

But some think this is an underestimation. McIntosh and his colleagues predicted a maximum sunspot number within the average range in their models, which are independent of NOAA. He said the NOAA forecast is “getting closer” to the average number of sunspots, if you look within the error bars.

The peak is expected to hit in October 2024, said Miesch, but the solar activity and sunspot number are predicted to stay elevated through at least mid-2025, according to January NOAA models.

But forecasting the sun’s behavior can be trickier than a Houdini routine.

“We understand a lot of things about the sun, but predicting when the maximum is going to arrive still has a reasonable amount of error on it,” said Rachael Filwett, a space physicist at Montana State University who was not involved in solar cycle forecasts.

But rest assured: Even if this solar maximum ends slightly below average or arrives later, that doesn’t mean it will be boring.

Will we see a big storm?

Sky watchers got a sampler of the sun’s bustle in 2023, as solar storms brought rare aurora sightings to lower-than-usual latitudes and disrupted radio signals. Other recent solar activity even knocked out smaller communications satellites from space.

Solar storms, referred to as geomagnetic storms as they collide with Earth’s magnetic field, are ranked on a scale of G1 (minor) to G5 (extreme). At least one geomagnetic storm last year ranked as a G4, the most intense storm to hit Earth in years.

The question for this solar maximum is: Will we see a G5 storm? The dramatic Halloween Storms in 2003, coming out of a past solar maximum, ranked as a G5.

“The key thing is the complexity of the [active] regions that are produced. It’s not about the number of spots,” said McIntosh. If the strong geomagnetic storms in 2023 are a harbinger, McIntosh said it looks “pretty good” to see more large storms.

When a large storm will happen is hard to pinpoint. Statistically speaking, McIntosh said it’s normal to see G4 and G5 events as the sun is coming out of its solar maximum. Some of the largest storms to ever hit Earth occurred during the declining phase of the cycle.

“Earth tends to see the opportunity for more direct hits as we’re coming down off of solar maximum because there are more sunspots at lower latitudes, closer to Earth’s location,” said Delores Knipp, a space physicist at the University of Colorado at Boulder.

Sunspots at the declining phase can be more complex, too, said Knipp. As the sun transitions into a solar minimum state, its sunspots migrate from its mid-latitudes to lower latitudes. Some research, she said, suggests this migration can cause crosstalk between the two hemispheres and create more magnetically complex eruptions on the sun.

That’s good news for aurora chasers because the chance of experiencing a large storm extends beyond the solar maximum — whether it occurs in 2024 or later — for another year or two.

Aside from auroras, the solar maximum will also provide unique opportunities for the upcoming total solar eclipse on April 8. Scientists say the sun will have many more particle streams coming from its outermost atmosphere (the corona) during totality, which eclipse watchers may be able to see.

“It’ll be a much, much more elaborate corona that we’ll see for the April eclipse,” Miesch said.

This article is part of Hidden Planet, a column that explores wondrous, unexpected and offbeat science of our planet and beyond.