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The culprit? A geomagnetic storm caused by high-energy particles and magnetism emitted from a sunspot—a blue-like discoloration on the sun’s surface. That same sunspot cluster that spent several weeks hiding on the back side of the sun is now spinning back toward Earth again.

More geomagnetic storms of varying strength are likely to occur in the next two weeks or so as the sunspot passes from left to right across the solar disk. (It takes about 27 days for the sun to rotate once.) Another extreme geomagnetic storm is unlikely to occur in the near future, but moderate to strong geomagnetic storms are not out of the question if a solar flare ejects a conveniently located sunspot cluster.

Technically, this is the third time this sunspot cluster has collided with Earth. It spent the first half of May heading our way and then returned at the end of the month in early June. Now Earth is once again in the line of fire.

Each time the sunspot cluster returns to the Earth-facing side of the sun, it is assigned a new number. In May it was “Active Region 3664”. Then the 3697. Now it’s the AR3723 — and it’s bursting with magnetism.

On Sunday, for example, AR3723 spat out an M-class solar flare. That’s the second-highest level on the scale (it becomes A, B, C, M, and X, with X-class flares being the largest). The pulse of radiation helped ionize Earth’s upper atmosphere, creating a reported shortwave radio outage over the Atlantic Ocean for several hours. And the AR3723 is poised to spit out more magnetic hiccups in the coming days and weeks.

Solar flares are intense explosions of high-energy particles and electrons that race through space at nearly the speed of light. They appear as intense bursts of light flickering in the sun. Sometimes slower-moving shock waves of magnetism, known as coronal mass ejections (CMEs), follow; they drift through space like interstellar tsunamis. If a CME hits Earth, its chaotic magnetism can interact with Earth’s magnetic field, producing aurora (and southern) episodes.

It’s too early to know exactly what the AR3723 offers.

It will take another day or so to spin into a better view of the observing satellites, which will help scientists at the Space Weather Prediction Center in Boulder, Colorado, better determine its magnetic structure. From there, scientists can make probabilistic predictions—projecting, for example, the chances of an M- or X-class solar flare within a given time frame. These eruptions send high-energy particles toward Earth, which can cause shortwave radio outages on the sunlit side of the planet.

The sunspot cluster is much smaller than it was before. But its magnetic structure is apparently still enough to spit out strong eruptions. The Center for Space Weather Prediction noted that AR3723 “remains the most magnetically complex group of spots” but hasn’t evolved much over the past day or so.