Saint Elmo’s Fire is far from being a variety of combustion associated with a heaven bound Muppet. Rather, it is an historic phenomenon observed by sailors at sea, and is named after the supposed patron saint of sailors, Erasmus.¹
Saint Elmo’s Fire has also appeared to pilots in connection with aircraft wings. Rarely, it is seen elsewhere. The single feature each of these occurrences shares in common is sharp or pointed surfaces.
The Nature of the Beast
Such surfaces do not provide fuel to some conflagration. In fact, they are generally metallic, and are not consumed at all. Saint Elmo’s Fire is an electrical and atmospheric phenomenon. It comes about because of a coronal discharge of electricity that leads surrounding atmospheric air to ionize, forming a plasma of positive ions. Forming along with those positive ions are negative electrons, with the emission of light. Don’t despair. A detailed explanation follows.
Coronal Discharge and Plasma
A coronal discharge involves the buildup of negative electrical charge, which eventually escapes through nearby gas atoms, producing a plasma and giving off high energy photons or, light — Saint Elmo’s Fire. Generally, the color of that light is blue to violet. This is due to the variety of atoms and molecules of gas most effected—the primary constituents being nitrogen and oxygen.
The Details, The “Skinny”
What produces the electric buildup? Friction between the vessel itself and Earth’s atmosphere. Air molecules pummel the vessel, stripping away a small number of their outer electrons. The remaining positive gas ions are large and heavy, so they do not adhere to the vessel, but instead continue as part of the atmosphere. The stripped electrons are very light and small and can stick to the vessel’s surface, imparting to it a negative electrical charge.
Encountering Saint Elmo’s Fire?
During thunderstorms, atmospheric charges are already high, so Saint Elmo’s Fire is common during those events. This is aptly portrayed in the YouTube video seen below.
1 In the Bible, saints are appointed God, not by any man. (Compare Romans 1:7)
Note: You might also enjoy What Factors Caused the 1840s Irish Potato Famine?
References:
So interesting to actually SEE the phenomenon on Youtube. Very different from a photograph or drawing.