Brilliant curtains of light shimmer over Norwegian mountains on February 14—part of a recent spate of auroras that caught sky-watchers by surprise. because the displays weren't linked to specific eruptions from the sun.
Space scientists think the light shows arose due not to specific solar eruptions but to common—but no less curious—"cracks" in Earth's magnetic shield.
Such cracks form when the sun's magnetic field lines interconnect with those of the Earth. For hours at a time, charged solar particles can spill through the openings, slam into atmospheric gas, and put on dazzling displays.
(Related: "Magnetic-Shield Cracks Found; Big Solar Storms Expected.")
Interactions between the field lines often occur when there's significant solar activity, which is precisely what the sun is experiencing now as it rolls toward solar maximum—the high point in our star's roughly 11-year cycle of magnetic fluctuations. Such peaks can trigger more and stronger outflows of solar particles.
"That activity is now picking up, and we'll begin seeing more and more of these geomagnetic events and storms than we have in the previous five years," said University of California space scientist Harald Frey, an expert on cracks in Earth's magnetic field, or magnetosphere.
Green "smoke" curls over houses in Bjarkøy, Norway, in a picture of the northern lights taken February 14.
Auroras occur when large numbers of charged particles from the sun encounter Earth's magnetic shield. Most of these particles get corralled toward the Poles, where they slam into atmospheric gases such as nitrogen and oxygen.
"It's the same concept as fluorescent light, really," said space scientist Marc Lessard of the University of New Hampshire. "Electrons in atmospheric molecules get excited, they bump up their energy and, as the atoms and molecules relax, they shoot off photons," creating the colorful light shows.
"There's a lot you can learn by just looking at the aurora," he added.
To better understand how solar storms might interfere with GPS systems, Lessard and his colleagues launched a sounding rocket into the aurora borealis from the University of Alaska's Poker Flat Research Range near Fairbanks on February 18.
Sounding rockets are small but powerful suborbital rockets that borrow their name from the marine term "to sound," which means to take measurements.
The recent project—conducted with help from NASA-sent the 46-foot-tall (14-meter-tall) rocket 217 miles (349 kilometers) into the aurora-filled sky to measure electrical and magnetic activity during the sky show.
(Related: "Aurora 'Power Surges' Triggered by Magnetic Explosions.")
Photograph by Lee Wingfield, NASA via AP
Reclining on a snowmobile, a sky-watcher in Karasjok, Norway, basks in the glow of the northern lights on February 20.
Especially intense auroras are often linked to solar eruptions called coronal mass ejections, or CMEs, which blast huge clouds of charged particles into space. Sun-watching satellites can see when a CME is aimed at Earth, often giving a day or two of advance warning for incoming solar storms.
A view from outside Fairbanks, Alaska, shows the recent aurora-bound rocket launch as the craft ascends hundreds of miles into the sky.
Lessard said the mid-February geomagnetic storm targeted by the launch was the result of an uptick in the part of the solar wind that's aimed at Earth. Solar wind is the flow of charged particles that's constantly streaming from the sun in all directions.
The sharp angles of a Norwegian barn contrast with the soft glow of northern lights, as seen in a long-exposure picture taken February 12 in the village of Ersfjordbotn.
Auroras are most often seen in high latitudes close to the Poles. But under the right conditions, very strong CMEs can trigger the light shows in regions closer to the Equator—a phenomenon that has been happening in recent months as the sun approaches solar max.