What is the weather phenomenon know as St Elmo's fire?

Answer 1

St. Elmo's fire is a electroluminescent coronal 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). Physically, St. Elmo's fire is a bright pink-purple glow, appearing like fire in some circumstances, often in double or triple jets, from tall, sharply pointed structures such as masts, spires and chimneys, and on aircraft wings. 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 Pollux. 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 Río de la Plata: "Everything was in flames, the sky with lightning, the water with luminous particles, and even the very masts were pointed with a blue flame."