The sun emitted a mid-level solar flare, peaking at 6:49 p.m. on June 7, 2013. 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 communications signals travel. This disrupts the radio signals for as long as the flare is ongoing, anywhere from minutes to hours.