A bolt out of the blue

Lightning has baffled physicists for decades bacause the electric fields inside thunderclouds do not appear to be strong enough to generate a conventional discharge of current. Researchers have recently discovered a new avenue for studying lightning, by examining the x-rays emitted as lightning streaks from theclouds to the ground. New observations of x-rays from lightning bolts supportthe hypothesis that lightning somehow accelerates electrons to nearly the speed of light in a phenomenon called runaway breakdown. An array of x-ray detectors are being built in Florida in order to study the processes that initiate lightning and allow it to propagate.