SAN FRANCISCO—The first 30 pixels of information ever recorded of a lightning bolt in the x-ray spectrum was presented as a video December 14 here at a meeting of the American Geophysical Union.


Despite being a common weather occurrence, lightning is still poorly understood as a natural phenomenon. Scientists are not sure what triggers a lightning bolt, how it moves down to the ground and how it strikes objects, said Joseph Dwyer, a physicist at the Florida Institute of Technology in Melbourne, during a press conference. Also unclear is how lightning emits x-rays and even gamma rays. The association of this highly energetic radiation with lightning was only discovered a decade or so ago.

To catch lightning in the act, Dwyer and his team built a dedicated x-ray detector. The size of a refrigerator, the device is a pinhole camera with 30 x-ray sensors arranged in a beehive pattern, and capable of capturing 10 million frames per second. The team launched small rockets into clouds to trigger lightning, and recorded the results for the first time this summer. "This is actually what Superman would see" if he watched lightning with his x-ray vision, Dwyer said.

The video shows pixels of x-rays lighting up along the path of the lightning—which propagates at one-sixth of the speed of light—as well as photons in the gamma ray spectrum. In the video, some of the gamma rays show up to the sides of the lightning's path because they can zip right through the camera's steel shielding, and thus they are not focused by the pinhole, Dwyer said.