February 6, 2011 — Late last month, a large sunspot group on the sun unleashed a massive solar flare. The flare sent charged particles to Earth, interacting with our atmosphere and causing beautiful auroral displays in the northern regions of North America, Europe and Asia. It also caused electrical power disruptions in various areas.

Sunspots are regions where the tangled magnetic field of the sun pokes through the surface, explained Edward Murphy, an astronomy professor in U.Va.'s College of Arts & Sciences.

"As the material in the sunspot radiates its energy into space, the magnetic field prevents new hot gas from moving in to reheat the cooling gas," he said. "Thus, sunspots are cooler – 5,000 to 7,500 degrees Fahrenheit – than the rest of the surface of the sun – 10,000 degrees Fahrenheit – and therefore appear darker.

"On occasion, the tangled magnetic field can snap, flinging particles off into space. If the Earth is along the path that the particles are ejected, they will hit our planet.

The particles are funneled along the Earth's magnetic field and hit our atmosphere near the north and south poles. As these solar particles hit the gas in our atmosphere, it excites them to glow, just like a fluorescent light bulb." The particles from the large flare that erupted around 11 p.m. EST on Jan. 22 started arriving 11 hours later, having traveled 93 million miles between the sun and Earth. The result was a large magnetic storm.

After a solar flare, "There is a minor chance that some auroral activity will be seen in the evening hours at mid-latitudes, such as Virginia," Murphy said. "If it occurs, it will most likely appear as a dull red or green glow in the northern sky."

Unfortunately, the January storm hit the East Coast early in the morning, so it wound down before darkness arrived. But Murphy noted that the sun should be very active over the next 12 to 18 months, so there should be future opportunities to see the aurora during this solar cycle. However, astronomers cannot predict when they will occur beyond a day or two in advance.

— By Fariss Samarrai