On August 9, 2011 beginning at 3:48 AM EDT, the sun emitted an Earth-directed X6.9 flare, as measured by the NOAA GOES satellite. These gigantic bursts of radiation cannot pass through Earth's atmosphere to harm humans on the ground, however they can disrupt the atmosphere and disrupt GPS and communications signals. In this case, it appears the flare is strong enough that it could cause some radio communication blackouts. It also produced increased solar energetic proton radiation -- enough to affect humans in space if they do not protect themselves.
There was also a coronal mass ejection (CME) associated with the flare. CMEs are another solar phenomenon that can send solar particles into space and affect electronic systems in satellites and on Earth. However, this CME is not traveling toward Earth and should not affect it.
AIA 304 movie (red one):
Credit: NASA/SDO/Helioviewer Caption: An x-class flare began at 3:48 AM EDT on August 9, 2011 and peaked at 4:05 AM. The flare burst from sun spot region AR11263, before it rotated out of view. The image here was captured by NASA's Solar Dynamics Observatory (SDO) in light at 304 Angstroms.
AIA 131 movie (blue one):
Credit: NASA/SDO/Helioviewer Caption: Shown here at short wavelengths of just 131 Angstroms—which are typically displayed in blue -- this movie from SDO offers an even more dramatic version of the Aug. 9 x-class flare.
