An Air Force crew captured video of rare St. Elmo's fire when they evacuated ahead of Idalia. What is this phenomenon?

Video captured by Air Force pilots evacuating ahead of Hurricane Idalia has gone viral because the storm appeared to create bolts of lightning sparking out of the aircraft. The stunning phenomenon isn't really lighting, though — it's St. Elmo's fire.

What is St. Elmo's fire?

The phenomenon usually occurs during a thunderstorm, when a very strong electrical current, comes into contact with a sharp object like the mast of a ship or tip of an airplane wing, said Jase Bernhardt, an associate professor and director of sustainability studies at Hofstra University. "The large number of electrons involved can glow for several minutes, like a neon sign," Bernhardt told CBS News via email. 

When this occurs on a ship, the National Oceanic and Atmospheric Administration advises "unprotected mariners should immediately move to shelter," because within five minutes after the glow begins, lightning may strike the mast. 

Bernhardt says that is based on the idea that, if there is a strong enough electrical charge in the atmosphere to cause St. Elmo's fire, then lightning may also develop in those conditions.

However, lightning and St. Elmo's fire are different. "Lightning is a direct movement of electrons from a cloud to the ground," he said, "while St. Elmo's fire is like a sparking effect, where electrons cover much less distance."

He said the phenomenon can also happen in other instances, like when a tall building has a pointed top, such as a lighthouse. "You just need a strong thunderstorm generating a strong electrical field and then the right type of object — doesn't have to be an airplane or ship," he said. "But, it seems to be most common for us to view this happening on a plane or ship, because they are often singular objects located in large, open spaces."

Bernhard says St. Elmo's fire should not be terribly dangerous to pilots since their planes are likely designed to withstand lightning and this phenomenon poses similar risks. The rare risk is of a power or systems issue, but larger aircraft like commercial and military planes are likely not at risk of this. 

MacDill Air Force Base video

Video shared by the MacDill Air Force Base in Tampa, an area greatly affected by the storm, shows the phenomenon in action. 

"All aircraft on the installation have been evacuated/secured in preparation for #HurricaneIdalia," states the post on X, formerly called Twitter. "During the evacuation, the 50th ARS recorded St. Elmo's fire, a weather phenomenon in which luminous plasma is created in an atmospheric electric field."

CBS News has reached out to a representative for the base and is awaiting response.

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