The sun is a solar flare machine, constantly spitting out waves of charged particles in all directions. Sometimes these hit Earth. Luckily we're protected by a strong magnetic field that directs the particles to the poles, which we experience as the Northern Lights, or Aurora Borealis.
But from time to time, the sun erupts in a massive superflare, also known as a CME or Coronal Mass Ejection. These can push our magnetic shield to its limits and actually cause electrical problems on the ground.
One of the worst instances of a CME striking the Earth occurred in 1859. It disrupted the telegraph system and sent sparks flying out of switchboards. It became known as the Carrington Event and begs the question - what if it happened today?