Northern lights dance over the Lyngan Alps in a picture taken Tuesday night near Tromsø, Norway. The brilliant auroras were triggered by a coronal mass ejection, or CME, that hit our planet Tuesday morning. A CME is a cloud of superheated gas and charged particles hurled off the sun.
When a CME hits Earth, the charged solar particles can interact with gases in our atmosphere to produce the northern and southern lights. Sky-watchers were put on alert for intense auroras Tuesday night through Wednesday morning.
Green auroras hang like storm clouds in the skies near Tromsø, Norway, on Wednesday.
This week's solar storm was strong enough to cause sporadic radio blackouts in high-latitude regions, spurring some airlines to reroute polar flights. Still, the storm is considered to be moderate and isn't expected to cause major disturbances to ground- or space-based equipment, experts said.
Photograph by Rune Stoltz Bertinussen, Scanpix/Reuters
A multicolored blade of light seems poised to strike over a snowy forest in Ivalo, Finland, on January 22. Late last week a NASA satellite witnessed a solar flare and CME from a different active region on the sun. That solar event triggered a round of auroras over the weekend, including the display captured above.
"At approximately 19:00 hrs the night sky over our Guest house was illuminated by the most spectacular display of Northern Lights, which lasted for several hours," photographer Andy Keen wrote on Spaceweather.com.
"The temperatures plummeted to a chilly -25 degrees Centigrade [-13 degrees Fahrenheit]—cold enough to make our lenses freeze and turn our camera bodies white."
Photograph courtesy Andy Keen
A snowmobiler stops to admire the northern lights in Finnish Lapland on January 24.
Improved computer models and a fleet of sun-watching satellites are helping space-weather experts better predict when CMEs will strike Earth—which also allows for more precise aurora forecasts.
"We went out with snowmobiles to wait for the incoming storm," photographer Antti Pietikäinen wrote on Spaceweather.com. "Show started slowly, and after 15 minutes the landscape was green!"
Northern lights flow over the snow-dusted mountains near Tromsø, Norway, on January 21. The stitched panorama picture also shows the auroras reflected in smooth ice, which is "normally ... covered by snow in winter time," according to photographer Thilo Bubek.
For instance, during the biggest solar storm on record—the 1859 Carrington Event—northern lights were reported as far south as Cuba and Hawaii, while southern lights were seen as far north as Santiago, Chile.
Photograph courtesy Pavel Kantsurov
Bright green auroras light up the night sky in a picture taken near Tromsø, Norway, on January 21.
The colors of auroras depend on the types of gases in Earth's atmosphere being affected by a solar storm. In most cases, auroral lights come from oxygen being "excited"—given extra electrical energy—during the collisions of gas atoms with solar particles. The charged-up oxygen releases the extra energy as green light.
Participants in a photo expedition work to capture the northern lights in Sweden's Abisko National Park on January 24.
"The auroras began as we were eating dinner and continued into the very early hours of the morning," expedition leader Chad Blakley told Spaceweather.com. "Words can not describe the excitement we shared and the sights we saw."
A composite picture from NASA's Solar Dynamics Observatory captured the January 19 solar flare erupting from the sun. The picture includes data from multiple wavelengths of ultraviolet light, to represent the different layers of the sun's turbulent atmosphere.
A blanket of green hangs over the coast of Bø in northern Norway in a picture taken January 6.
In general, auroras have been ramping up over the past year as the sun has approached what's known as solar maximum, a period of more intense activity in our star's natural 11-year cycle.
Scientists predict the sun will reach solar max in 2013, and that we'll continue to see more frequent and intense flares, CMEs, and other eruptions that—when aimed at Earth—might not only supercharge auroras but could also carry risks for airplanes, satellites, and the power grid.