What you should know about the St. Elmo’s fire phenomenon — and how to stay safe

By Jackie Wattles, CNN

(CNN) — It’s not just the title of a 1980s Brat Pack movie: St. Elmo’s fire is the name given to bright, sudden flashes of apparent lightning that can dance across a cloudy sky when thunderstorms are nearby.

Pilots shared footage of the phenomenon speckling the view outside their cockpit window on Tuesday as they evacuated from a Florida airbase in preparation for Hurricane Idalia. As the plane flew through the air, streaks of bright blue light appeared to zap the air outside, disappearing as quickly as they showed up.

Sailors have observed this feature of storms for centuries, according to a 2020 article about St. Elmo’s fire from the Massachusetts Institute of Technology’s news office. And they named it for St. Elmo, or Erasmus of Formia, the Christian saint of sailors.

The phenomenon is known is to occur when friction inside a storm cloud produces excess electrons, forming an electric field, according to MIT.

“If that field is strong enough, it can break apart surrounding air molecules, turning neutral air into a charged gas, or plasma,” the article states.

That commonly happens around pointy or sharp objects that are made of an electrically conductive material, such as radio or cell towers and the wings or windshields of airplanes.

When the sharp object “comes in contact with an extraordinarily high electrical field and a large number of electrons, the electrons can glow in various colors, like a neon sign, resulting in this rare phenomenon,” according to the United States National Oceanic and Atmospheric Administration.

The flashes tend to concentrate around pointy objects because they interact with “the electric field in a way that electrons are pulled from surrounding air molecules toward the pointed structures, leaving behind a veil of positively charged plasma immediately around the sharp object,” according to MIT.

That’s what causes the stringy flashes of blue or violet light.

Impacts of St. Elmo’s fire

The pilots who captured St. Elmo’s fire outside their cockpit window this week likely weren’t in any danger. St. Elmo’s fire on its own is not dangerous. And planes are equipped with devices designed to reduce electrical charge on their exterior surfaces, according to Encyclopedia Britannica.

Sailors even considered seeing the phenomenon a sign of good luck, a signal that St. Elmo was guarding their journey, according to Encylopedia Britannica.

But NOAA cautions that St. Elmo’s fire could be a warning sign, as it typically indicates that storms are nearby. And storms can bring actual lightning — which can be “mesmerizing but deadly.”

“Unprotected mariners should immediately move to shelter when this phenomena occurs,” the agency wrote about seeing St. Elmo’s fire on a ship. “Lightning may strike the mast within five minutes after it begins to glow.”

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