|The sun on 2/15/11 NASA SDO|
There are three categories of solar flares based on their brightness at wavelengths from 1-8 Angstroms. X-flares are major flares that can trigger planet-wide radio blackouts and long-lasting radiation storms. See this article on spaceweather.com for more information about solar flare classifications, and for updates as the flare heads toward earth. This eruption peaked at about 0200 Universal Time (1800 Central Time in the US) on February 15th. This is the largest solar flare in four years. Last autumn, NASA warned that a peak in the solar activity in 2013 could cause serious geomagnetic storms with the potential to knock out electricity grids for days to months.
Since this flare also sent a coronal mass ejection (CME) toward the earth, geomagnetic storms are possible when the CME arrives in 36-48 hours, although at the moment the prediction is that it is unlikely that there will be communications problems nor that the astronauts are in danger. Might be some great aurora as well!
Here's the link to an earlier article I wrote on "Solar activity (and Newt Gingrich)."