The flares were so powerful that "people in the northeastern U.S. could read newspaper print just from the light of the aurora," Daniel Baker, of the University of Colorado's Laboratory for Atmospheric and Space Physics, said at a geophysics meeting last December.

In addition, the geomagnetic disturbances were strong enough that U.S. telegraph operators reported sparks leaping from their equipment—some bad enough to set fires, said Ed Cliver, a space physicist at the U.S. Air Force Research Laboratory in Bedford, Massachusetts.

In 1859, such reports were mostly curiosities. But if something similar happened today, the world's high-tech infrastructure could grind to a halt.

It so happens that at least once during recorded history, a solar event of this magnitude did occur: the solar storm of 1859. On September 1 and 2 of that year, the largest geomagnetic storm in recorded history occurred, causing aurorae (the northern and southern lights) to be visible around the world. The Baltimore American and Commercial Advertiser wrote: "Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights…The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested."

Of course, the massive solar storm also caused damage, triggering telegraph malfunctions (even giving operators electrical shocks) and causing some telegraph pylons to suddenly spark and catch fire. A much smaller solar storm occurred in 1989, knocking out power throughout much of Quebec for over 9 hours, disrupting communications with several satellites in orbit and interfering with the broadcast of short-wave radio in Russia. Aurorae were reportedly visible as far south as Florida and Georgia; given the ongoing Cold War and the fact that many had never seen this phenomenon before, some feared that a nuclear strike was in progress.

I often think the risks of a geomagnetic storm are underplayed in the media. Severe geomagentic storms from solar eruptions are much more common then people realize -- there is a 1 in 100 chance of one happening any particular year.

While it's unlikely to damage consumer appliances, it could certainly would disrupt all forms of radio communication on earth, disable GPS, cellphones (which rely on GPS signals), and all others satellites, and if it's strong enough -- require utilities to shut-off the power grid to minimize damage from induced current on high-voltage transmission lines. NOAA carefully monitors solar storms, to notify utilities and government when a solar storm is likely to happen, so they can take emergency steps to overcome the impacts of magnetic radiation falling on the earth.