A bright blue or violet glow that emanates from tall, pointed structures such as lightning rods, ships’ masts, spires and chimneys, and sometimes airplane wings, during electrical storms. Sometimes a distinct hissing or buzzing sound accompanies the event. The “fire” is actually plasma, or ionized gas, caused during thunderstorms when the ground is electrically charged and the high voltage passes from clouds to the ground. The voltage separates the air molecules and the gas begins to glow.
Sailors who saw the phenomenon aboard ships and reacted with religious awe named it after St. Erasmus of Formiae (also known as St. Elmo), the patron saint of sailors. References to St. Elmo’s fire appear everywhere from the works of Julius Caesar and Pliny the Elder to Kurt Vonnegut’s Slaughter-House Five during the Battle of the Bulge.