University of Christchurch scientists John Abrahamson and James Dinniss believe the bright, hovering spheres first recorded in the Middle Ages are fluffy balls of burning silicon created by ordinary fork lightning striking the earth. "Most ball lightning is seen outside in thunderstorms, so we start with a normal lightning strike on soil," Abrahamson told BBC radio. "If you look at what the lightning does to the soil, it penetrates underneath the surface of the soil and we suggest the heating of the soil...brings about a hot vapor which then, after the lightning has gone, erupts above the ground in just the same manner as you blow air through your lips to get a smokers' puff," he said. Around one in 100 people claim to have seen ball lightning, but scientists have never been able to come up with a satisfactory explanation for it. It is typically described as having a diameter somewhere between a golf ball and a beach ball and lasting for around 15 seconds, floating in the air not far from the ground. Ball lightning can be any color, but is normally white or yellowish, with an intensity roughly equivalent to a 100 watt light bulb. In their article in Nature magazine, Abrahamson and Dinniss suggest that the extreme heat generated at the point where lightning strikes can sometimes turn the silica-carbon mixture contained in soil into silicon and silicon compounds with oxygen and carbon. The process is similar to the techniques used in industry to extract pure silicon from sand. The silicon forms tiny "nanoparticles" which link together into chains which are lifted above the ground by air currents, Abrahamson and Dinniss wrote. The particles then burn slowly, giving off heat and light. The scientists have not yet been able prove their theory by recreating ball lightning in the laboratory, but believe it explains all the commonly observed features of the phenomenon. |
|
 |