Magnetic activity around a sunspot region. From NASA's SDO spacecraft, AIA 171 channel. February 12-13, 2011.
This was a M 6.6 Category flare directed at Earth, seen at the very end of the video as a bright flash.
More info: Sunspots are areas where the Sun's internal magnetic fields "bubble up" and create cooler areas on the surface. Magnetic lines surround the depression carrying superheated solar plasma within them in arcing loops. Sometimes these loops lose stability and "snap", releasing solar particles outwards into space at hundreds of thousands of miles per hour. If they are aimed at Earth we experience it as a "solar storm", which has the potential to disrupt electronics and communications in orbit and on the ground. Only the most powerful solar storms can penetrate our magnetosphere to cause big problems, but they can create ionized particles in our atmosphere around the poles that glow brightly...a.k.a. the aurorae.
