High altitude lightning? I don't know if such a thing is possible, but this story I just ran across raises some interesting questions.
http://www.sfgate.com/cgi-bin/articl.../05/CAMERA.TMP
"Top investigators of the Columbia space shuttle disaster are analyzing a startling photograph -- snapped by an amateur astronomer from a San Francisco hillside -- that appears to show a purplish electrical bolt striking the craft as it streaked across the California sky. "