Above: Northern lights above Duke University. Image courtesy of Duke Office of Undergraduate Education.

If you were lucky enough to catch it, you might remember the sky turning a pinkish-green on an October evening just a few months ago. You might remember seeing the hurried frenzy of photos in your group chat, captions of “aurora borealis,” and shouts of “Come outside!” You might remember wondering—what causes the northern lights?

The answer is right above you. The sun is a huge bar magnet and therefore produces a strong magnetic field with its poles. Although its magnetic field initially appears roughly straight and parallel, the rotation of the sun alters the field’s direction. The sun isn't solid, so its equator rotates the fastest, while regions further away from the equator rotate slower. This difference in rotational speed is responsible for the characteristically colorful lights. With every rotation, the magnetic plasma making up the sun drags and twists the magnetic field, like a spoon dragging through honey.

The deformation of the sun’s magnetic field creates areas with stronger magnetic fields, more commonly known as sunspots. The lines near these regions can snap like a rubber band and produce an eruption. These magnetic contortions can produce solar flares, which are sudden flashes of light. Solar flares are accompanied by the release of huge clouds of electrically charged particles that travel millions of miles—some of which eventually strike the Earth.  

Above: The process of deformation of the Sun’s magnetic field. Image courtesy of Addison Wesley.

“These particles then slam into atoms and molecules in the Earth’s atmosphere and essentially heat them up,” explained Tom Kerss, an observer at the Royal Observatory in Greenwich, England. Indeed, the northern lights are simply atoms in the atmosphere colliding with particles from the sun, the “curtains” and “spirals” of light simply being the lines of force in Earth’s magnetic field.

But whilst the northern lights are breathtakingly beautiful, they possess a dangerous counterpart. In addition to solar flares, the sun can also produce coronal mass ejections (CMEs), which are huge masses of radiation and particles hurled in one direction. 

So what happens if a CME strikes Earth? You’d only have to look back to 1859. Known as the Carrington Event, the collision broke telegraph systems, caused fires, and electrocuted telegraph operators. The damages don’t seem catastrophic, but if a Carrington-sized impact hit us today, we wouldn’t be as lucky––our lives are more closely intertwined with technology than ever. There would be darkness everywhere as power grids would shut down and all electronic devices would seemingly fail overnight. As Dr. McIntosh, director of the High Altitude Observatory, put it, “All your infrastructure is toast…Could you imagine DC or New York City being without power for six months, or eight months a year?” Shockingly, a NASA-funded study finds that such an event would leave 130 million people without power and cost up to $2 trillion with a recovery time of four to 10 years.

Above: A composite image of a million-mile-long CME. Image courtesy of Andrew McCarthy.

So how great is the risk? Numerous solar storms have already struck Earth, and the largest one recorded narrowly missed Earth in 2012. In fact, physicist Pete Riley estimates the chances of a Carrington-size storm hitting Earth in the next decade are around 12%. As Dr. Kaku, a physics professor at CCNY noted in a Big Think video: “It’s Russian roulette, but it means that our society as we know it is potentially in danger.”

Of course, we cannot prevent a solar storm from occurring. Regardless, we can lessen the damage of an event with improved space weather forecasts. With satellites monitoring space weather and simulations predicting the effects of solar storms, we can garner more data to forecast a future solar storm. With ample warning, we could take measures to protect our satellites, astronauts, and power grids before they are struck by a CME. We could make CMEs as beautiful and as harmless as the northern lights. Technology has left us more vulnerable to a solar storm than ever, but it may also be the solution.