According to NASA, “A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released. Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to x-rays and gamma rays at the short wavelength end.” [What is a Solar Flare?]
The electromagnetic radiation from a particularly large solar flare could possibly damage satellites in orbit as well as electrical systems on the ground. The frequency and severity of solar flare varies with the eleven year solar cycle. We are currently near the maximum of that cycle, when flare are more common and more intense.
The largest known solar flare was observed, in 1859, by two astronomers, Richard C. Carrington and Richard Hodgson, studying sunspots. The light from the solar flare takes only minutes to reach the earth. But highly charged particles take much longer, from 12 to 40 hours, depending on how energetic the flare might be. In 1859, Carrington observed the flare just before noon on Thursday, and the charged particles hit the earth early the next morning:
“skies all over planet Earth erupted in red, green, and purple auroras so brilliant that newspapers could be read as easily as in daylight. Indeed, stunning auroras pulsated even at near tropical latitudes over Cuba, the Bahamas, Jamaica, El Salvador, and Hawaii. Even more disconcerting, 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.” [A Super Solar Flare]
A solar flare of similar intensity would be much more damaging today. The electrical grid in the U.S. and other nations is so immense that it is incomparable to the telegraph wires of the 1800′s.
“A super-storm has the potential to be a national disaster. With more than 80,000 miles of high voltage lines and 2,000 transformers supplying the nation’s electricity, the power grid is extremely vulnerable to a solar super-storm. Electrical currents from a major solar storm would overwhelm the transformers that control electricity to the grid. Tens of millions of people would be affected.” [Discovery.com Sun Storm FAQ]
Some moderate-sized solar flares have occurred in recent history:
“a huge solar flare on August 4, 1972, knocked out long-distance telephone communication across Illinois. That event, in fact, caused AT&T to redesign its power system for transatlantic cables. A similar flare on March 13, 1989, provoked geomagnetic storms that disrupted electric power transmission from the Hydro Québec generating station in Canada, blacking out most of the province and plunging 6 million people into darkness for 9 hours; aurora-induced power surges even melted power transformers in New Jersey.” [A Super Solar Flare]
The odds of a Super Solar Flare occurring soon are low. The largest known flare is still the 1859 event. But the odds of a flare of the same or greater size occurring eventually are very high. Solar flares are regular events; we don’t notice because usually the flares are relatively limited in intensity. But a major solar flare is bound to happen, sooner or later.