Dear Tom,
Has there been any definite word on the existence of, or even a definition of, “ball lightning”?
James Bathlow, Bolingbrook

Dear James,
The existence of ball lightning as a distinct phenomenon remains unproven. It is rare and unexplained. Ball lightning has been described as luminescent and spherical, ranging in size from pea-sized to several feet in diameter, hovering or floating, and lasting from a few to several seconds. Its color is generally white-ish, but other colors have been reported. The luminescent balls generally float at ground level. A number of hypotheses have been proposed to explain the existence of ball lightning, but none satisfactorily do so. If the phenomenon of ball lightning does actually exist, a satisfactory explanation has not yet been presented.