Tuesday, September 12, 2006

Ball Lightning???

This PH fascinates my husband more than myself, but it's definately worth mentioning! So you were going to ask what ball lightning is? Let me satisfy your curiosity.

From Wikipedia

Ball lightning reportedly takes the form of a short-lived, glowing, floating object often the size and shape of a basketball, but it can also be golf ball sized or smaller. It is sometimes associated with thunderstorms, but unlike lightning flashes arcing between two points, which last a small fraction of a second, ball lightning reportedly lasts many seconds. There have been some reports of production of a similar phenomenon in the laboratory, but some still disagree on whether it is a real phenomenon.

Laboratory experiments
Many attempts have been made over the years to produce ball lightning in the laboratory, but it is easy to mistake other phenomena for ball lightning. Most prominent among these are glowing spheres produced by high-energy arcs between metal electrodes. Such arcs often expel small droplets of molten metal that are heated to extremely high temperatures. Because of their high heat content, these droplets will continue to glow quite brightly for several seconds after landing on a floor or other surface, and their odd physical characteristics can cause them to roll, still glowing brightly, for some distance after landing. They thus mimic the most common description of ball lightning before cooling down into a small speck of metallic dust. The most familiar instance of these glowing spheres is the "weld spatter" usually seen during arc welding operations. The spheres can also be produced when a switch carrying very large electric currents is operated improperly, or during certain grinding or other machining operations.
Some laboratory experiments claim to have produced ball lightning, but there is no consensus that the phenomenon reproduced is related to the natural one. The natural occurrences are, by their nature, difficult to document accurately. Consequently, many scientists continue to dispute the existence of ball lightning as a distinct physical phenomenon.[7] In one such occurrence, Singer reports that staff at the Cavendish Laboratory, Cambridge apparently saw ball lightning, although Brian Pippard, the Head of Department, was skeptical of its reality.[8]
In February 2006, scientists at Tel Aviv University claimed to have produced ball lightning in the lab using a microwave drill and ceramic substrate.[9]. More recently (June, 2006) researchers at the Max Planck Institute for Plasma Physics successfully recreated the phenomenon using a relatively simple water tank experiment. The experiment involves two electrodes placed in a small tank of salt water, with one electrode covered by a clay tube. A large current of over 60 amps was then run through the water for 150 milliseconds, vaporizing water inside the clay tube and causing a ball of plasma to appear above the tank for 0.3 seconds. Although the plasma glows brightly it was found to be quite cold, much like a neon tube [10].

Ball Lightning Explained from News in Science

A New Zealand scientist may have finally explained the mechanism behind the extraordinary phenomenon of ball lightning.

Associate Professor John Abrahamson, a chemical engineer at the University of Canterbury in Christchurch, explains his theory in the April issue of Physics World Digest.

Ball lightning appears as a glowing, hovering ball of light that moves slowly near the ground before disappearing or exploding. The ball usually measures about 30 cm in diameter, although two park rangers in the Australian outback reported seeing one in 1987 that was 100 metres wide.

There are hundreds of theories about why ball lightning occurs, said Associate Professor Abrahamson — but according to his theory, there are several basic requirements.

The first is regular lightning. Second, the lightning must hit a structure such as a building, soil, or a tree. The struck object must have a metallic or an oxide component.

"Soil contains silicon oxide and carbon," Associate Professor Abrahamson explained. "The lightning reduces this to silicon metal, which is how we make silicon industrially."

The silicon vapour condenses to form silicon nanospheres, which collect together in long strings.

The third requirement is the presence of 'fulgerides' — long sausage-like holes in the soil full of hot vapour. These are created by lightning hitting the ground.

(Pic: Copyright Ern Mainka Photography. Used with permission.)
"The lightning strike on soil digs a hole in the ground, forming a very hot channel," said Associate Professor Abrahamson.

"Geologists have dug them up afterwards and found them to be made of frozen molten glass oxides, often in the form of tubes."

The silicon vapour is then ejected back out of the soil, forming a vortex ring — "like a smoker's puff" — which forms a sphere.

Once in this shape, the ball can move long distances, said Associate Professor Abrahamson.

"You have quite a robust structure, which continues to oxidise, and stays hot and visible," he explained.

The layer of oxide on the surface of each of the particles slows the process down, until eventually each particle runs out of metal. At this point the ball either fades away or explodes.

Ball lightning is not as dangerous as regular lightning, but it does carry very high levels of energy.

"People have been killed by ball lightning," Associate Professor Abrahamson warned.

"The metal in the high-energy balls will react with any water-containing substance, including flesh. If you touch ball lightning you could be severely burnt."

Understanding ball lightning is useful because its chemistry relates to that of ordinary lightning, he added.

"People haven't thought about the chemistry of ordinary lightning very much — this fills in that part of it."

A special issue of the Philosophical Transactions of the Royal Society in January 2002, edited by Associate Professor Abrahamson, added to more than 10,000 scientific reports on the subject of ball lightning.

Like all the other blogisodes, this one too will be updated from time to time as research is done. But please feel free to ask questions and make comments!


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