Many astronomy followers were fortunate to view the spectacular northern lights this past weekend when a rare phenomenon made them visible much farther south than usual.

Dr. Thomas Herring, director of Jack C. Davis Observatory at WNC, photographed the aurora borealis from his home and with an all-sky camera at JCDO.

“It takes very strong geomagnetic storms to produce bright enough auroras for us to see them,” he said. “It just so happens that the Sun is in a very active phase right now where its magnetic field is very complex and more likely to produce energetic ejections of material in the form of Coronal Mass Ejections (CMEs), which are usually associated with bright solar flares (an outburst of electromagnetic energy caused by collapsing magnetic fields on the Sun).”

Dr. Herring said that predicting bright viewing of northern lights is extremely difficult, even though a large number of sunspots on the Sun can serve as a forerunner to such an event.

“When we see a large number of sunspots on the Sun there is an increased likelihood of having flares and CMEs, but it is not certain which complexes of sunspots will result in such outbursts or when they will happen,” he said. “We can only get to more or less likely. The other complication is whether the outburst results in extra material being directed toward the Earth.”

Even then, the ejected plasma has to intercept the Earth in its orbit once it has traveled the vast distance from the Sun to the Earth's orbit.

“We were actually hit by a succession of CME events in a short period of time resulting in a very strong G5 geomagnetic storm last Friday,” Dr. Herring said.

Not since 2003 has the geomagnetic storm been so powerful, Dr. Herring said.

“The Sun goes through an 11-year cycle where its overall magnetic field direction flips around,” he said. “So, about every 11 or so years the likelihood of these storms impacting Earth goes up. However, we don't always get hit by the big CMEs.”

As a result, these geomagnetic storms are only known a few days in advance and the brightness of the auroras can only be discovered several hours ahead of time.