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It's coming back.

In mid-May, the brilliant Northern Lights, or aurora, were visible in places that rarely see them, due to powerful ejections from the sun colliding with Earth. These bursts of energy, such as solar flares or coronal mass ejections, are normal, especially as our medium-sized star has entered the peak of its activity cycle (it's an 11-year solar cycle). They came from a giant dark spot on the sun, called a sunspot, phenomena that tend to generate such solar bursts.

As the sun rotated, the spot faced away from us over the latter half of May. But now it's returning, and the astrophotographer Andrew McCarthy has been documenting this behemoth, dynamic zone. The large sunspot — which is some 15 Earth-diameters in size — is officially labeled "Region 3664."

"WOW! This is the same active region that caused those aurora a few weeks ago," McCarthy, who gave permission to Mashable to share his footage, marveled on May 28. "It’s finished rotating around the back of the sun and ready to cause some havoc again! This is the aftermath of yesterday’s X-class flare."

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X-class flares are the strongest class of solar flares, which are explosions of light from the sun's surface. The fact that this sun region is still producing potent flares means that more atmospheric radiance could soon be in store, depending on where the coming solar ejections hit. The active sun has also been producing coronal mass ejections (CMEs) — when the sun shoots a mass of super hot gas (plasma), essentially a chunk of the sun, into space. These drove the recent vivid Northern Lights.

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When they impact Earth, solar particles can become trapped by our planet's magnetic field, traveling to the poles and colliding with the molecules and particles in our upper atmosphere. Then, these atmospheric particles heat up and glow.

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Sunspots appear dark to us because they're "cooler" areas on the solar surface — meaning some 6,500 degrees Fahrenheit. These spots form where the sun's magnetic field — created by the vigorous movement of charged particles around the sun — is strong, which keeps some heat from the surface.

Crucially, these "magnetic field lines near sunspots often tangle, cross, and reorganize," NASA explains. This can lead to explosive solar flares or CMEs.

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It's not, however, all atmospheric radiance. These events can impact our vulnerable electrical and communications systems — if not properly prepared for.

During the May 2024 solar storms, many farming tractors, reliant on GPS satellite guidance systems, went offline. In 2003, airlines rerouted flights, at great cost, to avoid communication blackouts. In 1989, an extreme solar storm fried a $10 milliontransformer at Salem Nuclear Power Plant in New Jersey. The same CME knocked out power to millions in Québec, Canada, even trapping people in elevators.

Some more vigorous solar storms may indeed be on the way in 2024. If this activity impacts Earth, you could be in for some more lights. (Tip: Both the National Weather Service and National Oceanic and Atmospheric Administration provide aurora updates and forecasts.)

(责任编辑：知識)