A close-up in extreme ultraviolet light shows tight packs of coils around one active region on the sun in November 2013. The bundles of coils are charged particles swirling along magnetic field lines.
On dark, clear nights near the planet's poles, sky-watchers can often catch a glimpse of the sun's stormy activity. The undulating curtains of light that we call auroras are actually products of our star, created as charged particles from the sun slam into our atmosphere and cause atoms in the air to glow with vibrant colors. The best, most intense auroras appear when Earth is subjected to an onslaught from a solar flare.
These explosions of radiation from the sun are among the most powerful events in the solar system. Astronomers think solar flares happen when the sun's magnetic field lines get twisted and then release their pent-up energy in a sudden burst, sending out light in almost every wavelength across the spectrum, as well as accelerated subatomic particles such as electrons and protons.
Solar flares can last for minutes to hours, and if one is aimed at Earth, the resulting tidal wave of radiation can have a variety of impacts on our world.
Scientists classify solar flares based on how brightly they shine in x-rays, which in turn reveals some of their potential effects. The smallest C-class flares are barely perceptible on Earth, aside from the blast of light seen by x-ray satellites. Medium M-class flares can cause brief radio blackouts around the poles and minor solar storms. But the largest solar flares, called x-class events, can disrupt global events radio signals and cause stronger, longer-lasting solar storms.
Could a solar flare hurt us?
Aside from enhancing auroras, large solar storms are potentially hazardous to technologically driven lifestyles, since they can interrupt GPS signals, damage satellites, pose health risks to orbiting astronauts, and even carry the potential to knock out power grids.
The largest solar storm on record, known as the Carrington Event, happened in 1859. It triggered auroras as far south as Honolulu and Cuba—a rare event—and caused telegraph machines to shoot sparks and, in some cases, catch fire. Scientists estimate that if a similar solar flare hit Earth today, it would trigger widespread electrical blackouts and knock out global communications infrastructure, potentially causing modern society to grind to a halt.
Another powerful solar flare in 1967 almost triggered nuclear war, as U.S. military officers raced to determine whether a radio blackout was due to Soviet jamming signals or a natural event.
Recent research suggests that the damage caused by solar flares may depend not only on their strength, but on the types of rocks under affected areas. According to the U.S. Geological Survey, the different geology in a given region can either amplify or dampen the electrical interference caused by solar storms, increasing or decreasing risk to the local power grid.
Luckily, space agencies have sun-watching satellites in place that can see when solar flares happen and deliver warnings of incoming blasts. Such alerts can not only give time for power companies and astronauts to prepare for strong storms ahead, they can also provide space weather forecasts for the best times and places to see brilliant auroras dancing across the sky.