Last Tuesday, the Sun roared out a huge solar flare. NASA caught it on film, ranking it as a Class-M flare, just below the the most disruptive type of flare, Class-X.

NASA says it will give Earth a mere “glancing blow,” and the National Weather Service expects it will cause only minor disruptions to satellites and power grids.

For centuries, solar flares have been responsible for a multitude of earth-bound calamities, from blackouts to disrupted communications to strange lights in the sky. In 1859, the biggest flare on record hit, creating auroras worldwide and interrupting telegraph service for weeks.

http://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare/

Just before dawn the day after the 1859 flare, skies all over erupted in red, green, and purple auroras so brilliant that newspapers could be read as easily as in daylight.  Stunning auroras pulsated even at near tropical latitudes over Cuba, the Bahamas, Jamaica, El Salvador, and Hawaii. 

Telegraph systems worldwide went haywire. Spark discharges shocked telegraph operators and set the telegraph paper on fire. Even when telegraphers disconnected the batteries powering the lines, aurora-induced electric currents in the wires still allowed messages to be transmitted.

The sun is now entering a particularly active time, says NASA, and big flares like the one fromlast Tuesday will likely be common during the next few years, with solar activity expected to peak around 2013. Most solar flares will only cause minor problems with satellites and power grids, but there’s always a chance that a monster like the one from 1859 could hit.

“The worst-case scenario is an extreme event,” says Michael Hesse, chief of NASA’s Space Weather Laboratory at the Goddard Space Flight Center in Maryland. “If it were to happen and we don’t take any precautions, it would probably knock out our power grid for an extended period of time and destroy a sizable fraction of our satellite infrastructure.”

http://www.pcmag.com/article2/0,2817,2386623,00.asp