On May 12 and 13, two huge, powerful solar flares burst from the sun—and they're the most powerful flares to occur so far in 2013. You can see the phenomena, which came from a spot out of sight on the upper left side of the sun, in the stunning video below, which incorporates imagery from NASA's Solar Dynamics Observatory and from NASA and the European Space Agency's Solar and Heliospheric Observatory. (You can also see a prominence eruption on the sun's lower right side.)
These "X-Class" flares—what NASA calls the most intense solar storms—occurred just 14 hours apart. The number after the X provides information about its strength: X2 is twice as intense as X1, X3 is three times as intense, and so on.
The first flare registered at X1.7 and peaked at 10:00 p.m. on May 12; it was associated with a Coronal Mass Ejection (CME) that was not Earth-directed. The photo below blends two images from NASA's Solar Dynamics Observatory: One image shows light in the 171-angstrom wavelength, the other in 131 angstroms.
Then, at 12:05 p.m. on May 13, another flare occurred, this one X2.8-class. The image of that flare—the strongest flare so far this year—was captured by NASA's Solar Dynamics Observatory in light of 131 angstroms, which, according to NASA, is "a wavelength which is particularly good for capturing the intense heat of a solar flare and which is typically colorized in teal." Like the first flare, this one was associated with a CME that was not directed toward Earth.
Why are we seeing such intense activity? According to NASA, "Increased numbers of flares are quite common at the moment because the sun's normal 11-year activity cycle is ramping up toward solar maximum, which is expected in 2013."