Though they didn’t know it at the time, Galileo and his 17th-century rivals were the first to observe the sites of solar flares. What they saw through their crude telescopes were sunspots—dark patches on the solar disk where intense magnetic fields smother the upwelling of bright hot plasma.
Flares erupt near sunspots and hurl electrons and ions into the Sun’s atmosphere. When viewed with modern instruments in the UV and soft x-ray wavebands, sooty sunspots blaze in roiling turmoil.
According to decades of observation and theory, flares are fueled by twisted magnetic fields that snap into untwisted, lower-energy configurations (see Eugene Parker’s article in Physics Today, June 2000, page 26). But how pent magnetic energy propels electrons and ions remains a puzzle. Solar physicists expect a flare’s initial impulse to show up as gamma rays. Only recently, thanks to the launch last year of NASA’s Reuven Ramaty High-Energy...
