On the surface of the sun, giant fiery eruptions can send magnetically charged particles out into space. If these particles come in contact with Earth's magnetic field, they can have dangerous effects.
If a solar storm pierces Earth's atmosphere, it can send solar particles down onto the planet and weaken our protective magnetic bubble. The biggest solar storms can cause ripple effects in our power systems, heating and even destroying electrical infrastructure. That can send electronic communications haywire, and it's happened several times before.
The biggest, most dangerous solar storms are prompted by coronal mass ejections, which are essentially great balls of fire that shoot out from the sun. Scientists still aren't sure what causes these bursts, but they know they're related to the sun's magnetic field. Researchers can observe the bursts about eight minutes after they take off from the sun, which is how much time it takes signals to travel from the sun to Earth.
"The problem is we can’t control that large ball of garbage at the centre of the solar system," astrophysicist Scott McIntosh, who directs the High Altitude Observatory at the National Centre for Atmospheric Research, told Business Insider.
He said Earth's upper atmosphere is "wickedly" impacted by the sun's magnetic spewing, which can throw off our delicate modern balance of technology and metal wires.
"It's real even if you don't feel it every day," he said. "You might not, your banking institution might, your power grid company almost certainly does, and your telephone company absolutely does."
Space forecasters usually get between 17 and 36 hours of warning that a cloud of these dangerous particles is on its way to Earth from the sun. Then they run models to see where the impacts of the magnetic disturbances might land.
It's important lead time because electromagnetism drives a lot of our technology. When the Earth's magnetic balance is off, wires and cables don't work like normal, and satellites can even fall out of geosynchronous orbit.
McIntosh said the US government is so worried about these threats that it is aggressively stepping up a plan to build more super-transformers that can weather the geomagnetic storms.
"All your infrastructure is toast," he said. That can be especially true at higher latitudes and places where minerals underground have high conductivity, like the Northeastern US. "Could you imagine DC or New York City being without power for six months, or eight months a year because of a solar event that they didn't forecast well?"
Space forecasters who monitor the sun's activity from an observatory in Hawaii do their best to avoid that fateful scenario. They call power suppliers in vulnerable spots around the country whenever they think the Kp index (which measures geomagnetic activity) could pass a crucial threshold. Their recommendation is usually to crank down the voltage on the power lines for a few days to avoid blowing out transformers.
On average, federal forecasters say they alert power companies about dangerous incoming solar spinoffs about once a month. Usually, it all unfolds outside the awareness of the general public.
The Aurora Borealis can also be a sign that a solar storm is toying with the Earth's magnetic field. Typically, that spectacle is reserved for people near the poles. But when the light show starts to drift into more temperate latitudes, the dancing sky is giving us a hint that there are disturbances in the magnetosphere.
Perhaps the most infamous Earth-bound solar shot was the 1859 Carrington flare. The flare spread "northern" lights as far south as Hawaii.
"That was blowing up telegraph lines all over the world," McIntosh said.
Scientists have estimated that a great flare rivalling 1859's would cripple our modern energy grid, and that it could take $2 trillion (about R48 trillion) to rebuild big power systems in the first year of recovery.
In 2012, Earth narrowly missed a major solar storm as big as the Carrington flare.
"If the eruption had occurred only one week earlier, Earth would have been in the line of fire," astrophysicist Daniel Baker said after he published a study of the storm in 2013.
Other flares have impacted Earth more recently, though. In 1989, 6 million people in Quebec lost power for nine hours because of solar flare. Then there were the Halloween solar storms of October and November 2003, when 17 flares erupted on the sun at once. Airplanes were re-routed, spacecraft instruments were powered down, and the power went out in Sweden for about an hour, NASA said. That year, the northern lights were seen in Texas and Florida.
And just last year, when the trifecta of hurricanes Irma, Harvey and Maria were blasting the Caribbean and Gulf of Mexico, the Earth got slammed with the biggest solar flare we'd seen in a decade. As hurricane clouds were making it challenging for radio waves to travel efficiently, the sun doubled down and rendered ham radios (a staple of disaster relief work) temporarily useless.
While much of the sun's activity is still mysterious, we know that the big orange ball is operating on an 11-year cycle of high to low activity. Recently, the sun has been getting quieter with each cycle. Right now, we're at the lowest recorded solar minimum in 100 years. McIntosh predicts the next cycle will be 25% weaker than this. But a quiet sun is not a calm sun.
"The biggest geomagnetic storms come when the sun's very weak," he said.
A big solar storm could make modern life a mess, since without power, sewage can back up in cities. And what would happen if satellite-powered GPS is keeping a self-driving car on the road as a big solar storm hits?
"I’d hate to be like the boy that cried wolf," McIntosh said, "but if something bad did happen, could we cope?"
In 2014, physicist Pete Riley estimated that the odds of a big, Carrington-sized storm hitting the Earth in the next decade are about 12%. That's more than a one-in-ten chance.
McIntosh said we only know of one good way to weather a solar storm of that scale: "You batten down the hatches electronically, you power everything down, and try and ride it out. And you hope that when you come back up, it's still there."
Receive a single email every morning with all our latest news: Sign up here.
Also from Business Insider South Africa: