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Oct. 24, 2013

Picture of the Week: Ball Lightning

by Julie Leibach

Click to enlarge images
On August 24, 1895, about ten in the morning, in the midst of a storm of wind and rain, several persons saw descending to the ground a whitish-coloured globe of about an inch and a half in diameter, which, on touching the ground, split into two smaller globes. These rose at once to the height of the chimneys on the houses close by and disappeared. One went down a chimney, crossed a room in which were a man and a child, without harming them, and went through the floor, perforating a brick with a clean round hole of about the size of a franc.—from Thunder and Lightning, by Camille Flammarion (translated by Walter Mostyn), 1905. 
 
For centuries, people have related similar accounts to the one described above, entailing glowing spheres of red, yellow, orange, or white light, measuring between the size of a golf ball and a grapefruit, and capable of traveling slowly through the air or on the ground. These anecdotes likely describe a phenomenon loosely referred to as “ball lightning,” according to lightning expert Martin Uman, a professor of electrical and computer engineering at the University of Florida. The balls typically last for a second, luminescing constantly and not rising. Rather, “sometimes they fall and bounce,” says Uman—and when they do, they can even break into two.
 
The jury’s still out on what causes ball lightning. “There’s just an enormous literature of theories,” says Uman. Most of the time, it seems to be associated with garden-variety, cloud-to-ground lightning. For instance, ball lightning could result from the combustion of silicon—which is contained in soil—after lightning hits the dirt. But versions have also manifested from wall sockets and electrical machinery, according to Uman. In other words, he says, “ball lightning” could be considered more of a catchall term to describe a collection of electrically charged phenomena that, outwardly, appear similar but which manifest for a variety of reasons.
 
Attempts to recreate the phenomenon in the lab have been elusive. “We can’t do it on demand,” says Uman, although nature does it “in some very strange circumstances”—such as inside of airplanes (yes, airplanes), where the orbs have been documented “floating down the aisle.” Reporting in The Journal of Physical Chemistry this past June, a team working under the auspices of the U.S. Air Force Academy tried its hand at cooking up the glowing spheres. They ran electricity through an electrolyte solution and watched as a luminous, uniformly dense plasmoid—that is, a ball of ionized gas—rose from the pool. Yet, “ball lightning doesn’t rise,” says Uman.
 
Uman’s team has also made and published its own attempts. “We struck everything in the world with so-called triggered [with a rocket trailing a grounded wire] lightning that we could find, and we made some very interesting glows,” he says, “but all of them had the same characteristics in that they decreased in luminosity with time or did not otherwise resemble reported natural ball lightning”—except for one event: The team electrocuted a wet stainless steel plate, producing a glowing phenomenon above the plate that had a defined shape, didn’t rise, and which lasted for a half second—but it decreased in luminosity. “It may be the closest thing that anybody ever made [to ball lightning],” he says.
 
Ironically, while Uman has spent his career studying lightning, he has yet to see ball lightning in the wild (though his wife has). Accounts suggest that between one and 10 percent of the population has witnessed one, so it’s not exactly rare—yet, says Uman, it’s still “sort of a far-out phenomenon.” 

 

About Julie Leibach

Julie is the managing editor of ScienceFriday.com. She is a huge fan of sleep and chocolate. Follow her @julieleibach.

The views expressed are those of the author and are not necessarily those of Science Friday.

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