During the Age of Exploration, sailors knew that one meteorological phenomenon spelled disaster for their ships. It would manifest as an iridescence, an aura surrounding people or parts of their boats. Often, the effect would be accompanied by a hissing or buzzing sound, and jets of “flame” would jump from the mast or points of the ship.
This bizarre phenomenon, called St. Elmo’s Fire, was seen by some sailors as a portent of coming foul weather, and by others as a sign that they’d been blessed by the patron saint of sailors. So, what is St. Elmo’s Fire, what causes it, and why did so many sailors see it on their ships centuries ago? Let’s take a closer look.
The Science
St. Elmo’s Fire is a plasma discharge that can occur when atmospheric conditions create a strong electrical field. This means that the plasma in the corona discharge is mainly visible in bad storms or during volcanic eruptions when electrical and magnetic fields are at their strongest. Often, the luminous effect is most visible on high, pointed objects, like animal horns, masts, spires, or tall buildings. Sometimes, the luminous effect can even be seen around people.
Objects in electrical fields can have their surrounding air molecules ionized. The reason this effect occurs most commonly at points is that electrical fields are stronger in areas of high curvature, meaning that lower voltage is required to produce ionized plasma at the points of structures instead of on flat surfaces.
Notably, the luminescence of St. Elmo’s Fire functions on similar principles as neon lights do. However, the color of the naturally occurring St. Elmo’s Fire tends to be blue or purple because of atmospheric gasses, whereas neon lights can burn different gasses to create different colors.
In History
Sailors saw the effect often due to the near-perfect conditions of a ship on the ocean for generating an ionized plasma charge. Sailing through the ocean makes it more likely that you will encounter a thunderstorm with nothing else around to discharge its energy into. Typically, a ship at sea is the only tall structure for a thunderstorm to act upon. The high masts and plentiful pointed structures gave sailors many opportunities to see St. Elmo’s Fire at play across their ships.
While some sailors considered the appearance of these jets of plasma to be a good omen, others considered them troubling, as they indicated the coming of foul weather. A lightning bolt striking the main mast of a sailing vessel is a death sentence for all sailors aboard the boat, and St. Elmo’s Fire often occurs before such lightning strikes occur.
Notably, the word “corposant,” which refers to the plasma jets of St. Elmo’s Fire, or just luminous phenomena, is derived from a similar religious background as the common poetic name. “Corpo” is Latin for “body,” while “sant” means saint or holy. As such, the original etymology of this term literally means “holy body,” lending a supernatural explanation to something that science can now explain with certainty.
