On April 2, 2014, the sun emitted a mid-level solar flare, peaking at 10:05 a.m. EDT, and NASA's Solar Dynamics Observatory captured imagery of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.
This video from NASA's Solar Dynamics Observatory shows the flare in a blend of two wavelengths of extreme ultraviolet light: 304 angstroms and 171 angstroms, colorized in red and yellow, respectively.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 8.0.0.0.0