Some 13,000 years ago, the Sun emitted a huge belch of radiation that bombarded Earth and left its imprint in ancient tree rings. That solar storm was the most powerful one ever recorded. The next strongest was the 1839 Carrington Event. It was spurred by a huge solar flare that triggered a powerful geomagnetic storm at Earth. The resulting "space weather" disrupted telegraph communications around the world. Today, as we move through this year's "solar maximum", a period of solar activity that occurs every 11 years, scientists want to prepare governments for the effects of severe solar storms.