What Is Saint Elmo's Fire?
Saint Elmo's fire is a flash of light, most likely produced by an electrical discharge. It forms around tall, grounded metal objects, such as ship's masts, antennae, and chimney tops.
Because Saint Elmo's fire often occurs during thunderstorms, it has been suggested that the source of the electrical buildup is lightning. Another theory is that Saint Elmo's fire is initiated by weak static electricity, created when an electrified cloud touches a tall metal object. Molecules (particles made by the combination of two or more atoms) of gas in the air around the object then become ionized (take on an electrical charge) and glow.
This phenomenon was first described by sailors, who witnessed the display of spearlike or tufted flames on the tops of their ships' masts. It was named for Saint Elmo (originally called Saint Ermo), the patron saint of sailors.
Sources: Forrester, Frank. 1001 Questions Answered About the Weather, pp. 182-83; Schaefer, Vincent J., and John A. Day. A Field Guide to the Atmosphere, p. 196.