December 19, 2012

St. Elmo’s Fire Can Be Ghostlike

Q:  Sometimes you hear of something called St. Elmo’s Fire. What is it?

A: It’s one of nature’s more unusual displays, says Brent McRoberts of Texas A&M University. When skies are stormy and lightning is present, St. Elmo’s Fire can occur. “It’s an electrical discharge in the air and instead of appearing like a lightning bolt, it appears like a glow around an object, especially tall ones like church steeples or masts on ships,” he explains. “It is scientifically known as a corona or point discharge, where the electrical field strength reaches 1,000 volts per centimeter. It can only occur during an electrical storm. When a thunderstorm occurs, the air between the clouds and the ground can become statically charged, resulting in a ‘glow discharge.’ It’s different from lightning in that it is continuous and its glow around an object can last for several minutes. It’s the same principle used to create fluorescent tube lighting.”

St. Elmo's fire

St. Elmo's fire can create eerie images

Q: Has it been around a long time?

A: For thousands of years, but it has been called different names and described in many ways, adds McRoberts. It is named after Saint Elmo, the patron saint of sailors. St. Elmo’s Fire was mentioned in one of Julius Caesar’s “Commentaries,” also in Herman Melville’s “Moby Dick” and other works, and Ben Franklin noticed its appearance around steeples during his experiments with lightning. “It’s usually described as a blue or bluish-white glow attached to an object, and sometimes this gives off a very eerie, ghost-like appearance,” he adds. “Sailors considered it a good omen. Today, it can also appear on the wings of airplanes and propellers, and it can disrupt radio transmission. It sounds like a hissing noise on radio receivers, according to many pilots.”

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Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.

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