St. Elmo's fire

St. Elmo's fire (also St. Elmo's light) is a weather phenomenon in which luminous plasma is created by a coronal discharge from a sharp or pointed object in a strong electric field in the atmosphere (such as those generated by thunderstorms or created by a volcanic eruption).

St. Elmo's fire is named after St. Erasmus of Formiae (also called St. Elmo, the Italian name for St. Erasmus), the patron saint of sailors. The phenomenon sometimes appeared on ships at sea during thunderstorms and was regarded by sailors with religious awe for its glowing ball of light, accounting for the name.Because it is a sign of electricity in the air and interferes with compass readings, sailors also regarded it as an omen of bad luck and stormy weather.

Physically, St. Elmo's fire is a bright blue or violet glow, appearing like fire in some circumstances, from tall, sharply pointed structures such as lightning rods, masts, spires and chimneys, and on aircraft wings. St. Elmo's fire can also appear on leaves, grass, and even at the tips of cattle horns.Often accompanying the glow is a distinct hissing or buzzing sound. It is sometimes confused with ball lightning.

St. Elmo's fire is a mixture of gas and plasma, as are flames in general and stars. The electric field around the object in question causes ionization of the air molecules, producing a faint glow easily visible in low-light conditions. Approximately 1000 volts per centimeter induces St. Elmo's fire; however, this number is greatly dependent on the geometry of the object in question. Sharp points tend to require lower voltage levels to produce the same result because electric fields are more concentrated in areas of high curvature, thus discharges are more intense at the ends of pointed objects. Conditions that can generate St.Elmo's fire are present during thunderstorms, when high voltage levels are present between clouds and the ground underneath. Air molecules glow due to the effects of such voltage, producing St. Elmo's fire. The nitrogen and oxygen in the Earth's atmosphere causes St. Elmo's fire to fluoresce with blue or violet light; this is similar to the mechanism that causes neon lights to glow.