Australian scientists have come up with a new theory to explain the eerie phenomenon known as ball lightning.
Such balls of flame – usually the size of a grapefruit and lasting up to twenty seconds – have been seen for hundreds of years. Explanations have ranged from black holes, UFOs and antimatter to hallucinations.
Now, though, CSIRO and Australia National University scientists have a mathematical theory to explain how and why it occurs.
The theory focuses on how ball lightning occurs in houses and aeroplanes as well as outdoors, and how it can pass through glass. It's caused when leftover ions, which are very dense, are swept to the ground following a lightning strike, says CSIRO scientist John Lowke.
"A crucial proof of any theory of ball lightning would be if the theory could be used to make ball lightning. This is the first paper which gives a mathematical solution explaining the birth or initiation of ball lighting," he says.
The phenomenon occurs in houses and aeroplanes when a stream of ions accumulates on the outside of a glass window and the resulting electric field on the other side excites air molecules to form a ball discharge. The discharge requires a driving electric field of about a million volts.
Lowke cites eye-witness accounts of ball lightning, also known as St Elmo's Fire, by two former US Air Force pilots to support his theory.
"After flying for about 15 minutes, there developed on the randome [radar cover] two horns of Saint Elmo's fire," says former US Air Force lieutenant Don Smith. "It looked as if the airplane now had bull's horns...they were glowing with the blue of electricity."
Lowke's paper, he says, gives the first mathematical solution explaining the initiation of ball lightning using standard equations for the motion of electrons and ions.