For the 1980s brat pack movie, see St. Elmo's Fire (movie).

St. Elmo's Fire on a ship at sea

St. Elmo's Fire is an electro-luminescent discharge caused by the ionization of the air during thunderstorms inside of a strong electric field. Although referred to as "fire", St. Elmo's Fire is in fact a kind of plasma caused by massive atmospheric potential differences.

Observation

St. Elmo's Fire is named after Erasmus of Formiae (also called St. Elmo), the patron saint of sailors (who held its appearance to be auspicious). Physically, it is a bright bluish-white glow, appearing like fire in some circumstances, often in double or triple jets, from tall, sharply-pointed structures such as masts, spires and chimneys.

It is named such because the phenomenon commonly occurs at the mastheads of ships during thunderstorms at sea. Benjamin Franklin correctly observed in 1749 that it is electric in nature. St. Elmo's Fire can also appear between the tips of cattle horns during a thunderstorm, or sharp objects in the middle of a tornado, but is not the same phenomenon as ball lightning, although they are related. In ancient Greece, the appearance of a single one was called Helena and two were called Castor and Pollux.

Other works

References to St. Elmo's Fire, often known as "corposants" or "corpusants" from the Spanish Cuerpos Santos (Holy Bodies), can be found in the works of Julius Caesar, Pliny the Elder, Herman Melville, and Antonio Pigafetta's journal of his voyage with Ferdinand Magellan.

"'Look aloft!' cried Starbuck. 'The corpusants! The corpusants!' All the yard-arms were tipped with a pallid fire; and touched at each tri-pointed lightning-rod-end with three tapering white flames, each of the three tall masts were silently burning in the sulphurous air, like three gigantic wax tapers before an altar." – Herman Melville, Moby Dick.