Will Sullivan

Daily Correspondent

Sky-watchers around the world were treated to rare, dazzling displays of the northern lights over the weekend, as the glowing phenomenon, which is usually seen close to the Arctic Circle, was visible much farther south than usual.

Powerful solar storms triggered a light show that astonished viewers in Great Britain, Poland, Siberia and Mongolia, as well as from Oregon and Washington to Texas and Florida in the United States.

“The solar eclipse last month, I thought that was the coolest thing I’d ever seen,” Benjamin Williamson, who saw the aurora from Portland Head Light in Maine, says to the New York Times’ Katrina Miller, Ivan Penn and Emmett Lindner. “This might have beat it.”

Aurora borealis, or the northern lights, are caused by interactions between charged particles from the sun and Earth’s atmosphere. Every second, the sun releases about one million tons of charged particles, including protons and electrons, that travel outward in a stream of plasma known as the solar wind.

When these particles reach our planet, some get trapped in its magnetic field, which redirects them toward the poles. There, they collide with oxygen and nitrogen in Earth’s upper atmosphere, raising these molecules’ energy level. The molecules then release that energy in the form of glowing auroras.

But the aurora activity over the weekend was unusual: Beginning Friday, scientists observed a series of intense explosions of plasma and magnetic fields from the sun’s atmosphere known as coronal mass ejections. The activity stemmed from a cluster of sunspots around 17 times the diameter of Earth. As of Friday, experts had seen at least seven coronal mass ejections heading toward our planet.

When these blasts of solar activity are pointed toward Earth, they can result in intense geomagnetic storms—and on Friday evening, Earth experienced an extreme (G5) geomagnetic storm for the first time since October 2003. A watch for strong (G3) and severe (G4) geomagnetic storms continued throughout the weekend.

The historic storm—a major disturbance in the magnetosphere—led to reports of power grid irregularities and disruptions to high-frequency communications, GPS and satellite navigation.

But it also made the northern lights visible at lower latitudes than usual. With the weekend’s geomagnetic storms, the glowing display was visible over wide areas of the U.S. Auroras are typically only seen as far south as Florida around once per decade, but some residents of the Sunshine State were able to spot the northern lights. Still, cloud coverage in some parts of the country blocked the view of the sky.

The northern lights can appear with a few different colors, depending on the type of gas the solar particles interact with. Auroras appear greenish-yellow or red when they’re emanating from oxygen and blue when nitrogen is the trigger.

Here are 12 images of the northern lights, as seen from around the world over the weekend.

purple sky with pink lights and green along the horizon over water
Pink, purple and green hues glow above San Francisco's North Bay, as seen from China Camp Beach in San Rafael, California, on May 11. Tayfun Coskun / Anadolu via Getty Images
people stand along a railing taking pictures of the green-streaked sky with their phones and cameras
Spectators gather in front of a green-streaked sky on May 10 in Whitley Bay, England. Ian Forsyth / Getty Images
purple and red colors in a nearly cloudless sky over slightly bare trees, with a yellow glow near the horizon
The northern lights glow over a farm on the outskirts of Bloomington in southern Indiana on May 10. Jeremy Hogan / SOPA Images / LightRocket via Getty Images
the sky appears mostly purple over the Great Wall of China, with a bit of pink and orange on the left horizon
The aurora borealis turns the sky purple and pink over the Badaling section of the Great Wall in Beijing, China, from the night of May 11 into the morning hours of May 12. Yang Dong / VCG via Getty Images
pink sky with streaks of green above a dark horizon with trees
The northern lights illuminate the sky above a horse pasture in Mercer, Maine, on May 10, bringing pink, orange and green hues to the cosmos. Michael Seamans / Getty Images
colors stream down from the sky like rays of sun over a small lighthouse on the coast at the center bottom of the frame
Above St. Mary's Lighthouse in Whitley Bay on the coast of England's North East region, the sky glows in purple, blue, green and orange on the first night of the unusual auroras, May 10. Owen Humphreys / PA Images via Getty Images
a haze of pink and green over dark evergreen trees
The aurora borealis shines over trees in Manning Park, British Columbia, Canada, on May 11. Andrew Chin / Getty Images
a dark haze of green in the sky above a lake
The northern lights appear in green above Rochester, New York, on May 11. Lokman Vural Elibol / Anadolu via Getty Images
two people, their backs to the camera, sit overlooking a city and mountains with bright pink sky shining through sparse clouds
Bright pink sky shines through sparse clouds above Smlednik, Slovenia, on May 11, as spectators sit and watch. Luka Dakskobler / SOPA Images / LightRocket via Getty Images
layers of purple, green and pink light shine in waves above trees
From Latourell, Oregon, the northern lights appear as ribbons of color in the night sky on May 11. Mathieu Lewis-Rolland / Getty Images
glowing lights cover the left half of the sky above a city at night
The atmosphere shines in pink, blue and green on May 11 above city lights in Vienna, Austria. MAX SLOVENCIK / APA / AFP via Getty Images
the sky is nearly entirely pink over a mountain with sparse vegetation sticking up from it
Above Lake Berryessa in California, west of Sacramento, the northern lights turn the sky pink on May 11, around midnight. Carlos Avila Gonzalez / San Francisco Chronicle via Getty Images

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Will Sullivan

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.