St. Elmo’s fire — also called Witchfire or Witch’s Fire — is a weather phenomenon in which luminous plasma is created by a corona discharge from a rod-like object such as a mast, spire, chimney, or animal horn in an atmospheric electric field. It has also been observed on the leading edges of airplanes.
The intensity of the effect, a blue or violet glow around the object, often accompanied by a hissing or buzzing sound, is proportional to the strength of the electric field and therefore noticeable primarily during thunderstorms or volcanic eruptions.
St. Elmo’s fire is named after St. Erasmus of Formia, the patron saint of sailors. The phenomenon, which can warn of an imminent lightning strike, was regarded by sailors with awe and sometimes considered to be a good omen.