Solar flare of February 15, 2011, as captured by the SOHO and SDO spacecraft. Image credit: NASA

The strongest solar flare in more than four years erupted on the sun at 0156 UTC on Tuesday, when giant sunspot 1158 unleashed an X2-class eruption. X-class flares are the strongest type of x-ray flare, and this week's flare is the first X-class flare of the new 11-year sunspot cycle 24, which began in 2009 - 2010. The flare was accompanied by a Coronal Mass Ejection (CME), which means that a portion of the sun's atmosphere was ripped away and thrown into space. High-energy particles from the CME arrived at Earth at 01 UTC this morning, and sky watchers at high northern latitudes may be able to see auroras over the coming few nights.

Jeff Masters