St. Elmo's fire is an electro-luminescent corona 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 low density, relatively low temperature plasma caused by massive atmospheric electrical potential differences which exceed the dielectric breakdown value of air at around 3 megavolts per meter. St. Elmo's fire is named after Erasmus of Formiae (also called St. Elmo), the patron saint of sailors (who sometimes held its appearance to be auspicious).
It is named such because the phenomenon commonly occurs at the mastheads of ships during thunderstorms at sea, and St. Elmo is the patron saint of sailors. Benjamin Franklin correctly observed in 1749 that it is electric in nature. It is said that St. Elmo's fire can also appear from 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 possibly related. In ancient Greece, the appearance of a single one was called Helena and two were called Castor and Polydeuces.
Charles Darwin noted the effect while aboard the Beagle and wrote of the episode in a letter to J.S. Henslow that one night when the Beagle was anchored in the estuary of the Rio Plata: "Everything was in flames, the sky with lightning, the water with luminous particles
There is a possible reference to St. Elmo's fire in Samuel Taylor Coleridge's The Rime of the Ancient Mariner:
A representation of St. Elmo's fire on cows' horns is seen near the end of Part 1 of the television adaptation of the Pulitzer Prize-winning novel Lonesome Dove by Larry McMurtry.
Electrical phenomena | Nautical lore | Plasma physics | Storms | Atmospheric electricity | Lightnings
Elmsfeuer | Fuego de San Telmo | Feu de Saint-Elme | Fairo di Santa Elmo | Fuoco di Sant'Elmo | Corpus sanctum | セントエルモの火 | Elmsvuur | Sankt Elms ild | Ognie świętego Elma | Fogo de São Telmo | Огни святого Эльма | Elmon tuli | Sankt Elmseld | 聖艾爾摩之火
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