Ball lightning is a natural phenomenon associated with thunderstorms and takes the form of a long-lived, glowing, floating object, as opposed to the short-lived arcing between two points seen in common lightning. An early attempt to explain ball lightning was recorded by Nikola Tesla on March 5, 1904 (Electrical World and Engineer). 
Ball lightning discharges were once thought to be an extremely rare occurrence, but recent research shows that a few percent of the US population have been witnesses (Uman.) Ball lightning is photographed very rarely, and details of witness accounts can vary widely. Many of the properties observed in ball lightning accounts conflict with each other, and it is very possible that several different phenomena are being incorrectly grouped together. The discharges can appear during thunderstorms; sometimes issuing from a lightning flash. But large numbers of encounters occur during good weather with no storms within hundreds of miles. Ball Lightning tends to float (or hover) in the air and take on a ball-like appearance. The shape can be spherical, ovoid, teardrop, or rod-like with one dimension being much larger than the others. The longest dimension observed is between fifteen and forty centimeters. Many are red to yellow in color, sometimes transparent, and some contain radial filaments or sparks.
Sometimes the discharge appears to be attracted to a certain object, and sometimes to move randomly. After several seconds the discharge leaves, disperses, is absorbed into something, or, rarely, vanishes in an explosion.
One report described ball lightning engulfing and following a car, causing the electrical supply to overload and fail.
Ball lightning usually appears in a thunderstorm, and has been seen in places as diverse as "escorting" World War II bombers, flying alongside their wingtips. During this period, due to the enigmatic nature of this phenomenon, these appearances were referred to as "foo fighters." Other accounts place ball lightning as appearing over a kitchen stove to wandering down the aisle of an airliner.
One of the earliest recorded, and most destructive, occurrences is thought to have taken place during The Great Thunderstorm at Widecombe-in-the-Moor, Devon, in the United Kingdom, on October 21 1638. Four people died and around 60 were injured when what appears to have been ball lightning struck a church.
Another reference to ball lightning appears in Laura Ingalls Wilder's book "On the Banks of Plum Creek" [Harper Trophy, 1937] in which the lightning appears during a thunderstorm near a cast iron stove in the family's kitchen. It is described as appearing near the stovepipe, then rolling across the floor, only to disappear as the mother chases it with a willow-branch broom.
For a long time the phenomenon was treated as myth. Although the exact nature of the phenomenon is still the subject of speculation, there is now agreement that it is neither mythical nor purely psychological. Surveys have been taken of eyewitness accounts by at least 3000 people, and it has been photographed several times. There is as yet no widely accepted explanation for ball lightning.
Some difficult features to explain are the longevity of existence and the near neutral buoyancy in air. It may be that the energy is feeding the glow by a stored chemical form and slowly released. There have been many attempts to create ball lighting in the laboratory, and some have resulted in superficially similar phenomeina, but there have been no convincing demonstrations that the natural phenomenon has been reproduced.
A popular hypothesis is that ball lightning is a highly ionized plasma contained by self-generated magnetic fields. Upon closer examination, this hypothesis does not appear to be tenable. If the gas is to any reasonable degree ionized and if it is anywhere near thermodynamic equilibrium, then it must be very hot. Since it must be in pressure equilibrium with the surrounding air, it would be much lighter than air and hence float up rapidly. Adding magnetic fields can help solve the problem of the coherence of the plasma blob, but will make it even lighter. (The proof of this is the virial theorem as applied to plasmas and fields.) In addition, a hot plasma, even if combined with magnetic fields, would not last nearly as long as ball lightning is reported to, both because of recombination and heat conduction.
There may, however, be special forms of plasma for which the above arguments do not fully apply. In particular, a plasma may be composed of negative and positive ions, rather than electrons and positive ions. In that case, the recombination may be rather slow even at ambient temperature. One such theory involves positively charged hydrogen and negatively charged nitrites (NO2–) and nitrates (NO3–). In that theory, the role of the ions as seeds for the condensation of water droplets plays an important role.
Ball lightning has also seen to appear inside an aircraft, which has an metallic skin. Since the electric field cannot penetrate metal, there is a possiblity ball lightning could be some form of induction phenomena.
The natural phenomenon of ball lighting has been reportedly the source of some reports of supernatural phenomena, ranging from will o' the wisps to UFOs. Some people believe the ball lightning phenomena are ghosts or spirits. References can be seen in the will o' the wisp and other spirits that take the guise of orbs of light. Some UFO skeptics have suggested that many apparent close encounters are actually observations of ball lightning. UFO enthusiasts report seeing ball lightning often at crop circle sites and believe them to be some kind of intelligence or come from some kind of intelligence while not denying that it is indeed ball lightning.
- "...Our conclusion is that these fireballs are primarily RF in origin, and not nuclear phenomena..." - Corum
- "...No theory of ball lightning exists which can account for both the degree of mobility that the ball exhibits and for the fact that it does not rise...." - Talbot
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- Golde, R. H. Lightning. Bristol: John Wright and Sons Limited. 1977.
- Golde, R. H. Lightning Volume 1 Physics of Lightning. Academic Press. 1977.
- Singer, Stanley. The Nature of Ball Lightning. New York: Plenum Press. 1971.
- Stenhoff, Mark. Ball Lightning, An Unsolved Problem in Atmospheric Physics. New York, Boston,Dordrecht, London, Moscow: Kluwer Academic/Plenum Publishers. 1999.
- Uman, Martin A. Lightning. Dover Publications 1984.
- Viemeister, Peter E. The Lightning Book. Cambridge: MIT Press. 1972.
- Bergström, Arne, "Electrodynamic confinement - - a new field of science and technology ? (the secret of ball lightning and a new field of science and technology)". Scientor Research & Development. Stockholm, Sweden.
- Corum, Kenneth L., and James F.Corum, "Tesla's production of electric fireballs". Corum & Associates, Inc., Windsor, Ohio
- Talbot, Michel T., "Ball Lightning : Rare Atmospheric Phenomena (RAP)"
- Bill Beaty's Ball Lightning Page and Eyewitness reports
- Various articles, experiments, and information on Ball lightning
- Hochwald, Hans, "Microwave Experiments" Alternative "toaster".
- 'Ball Lightning' produced using a high voltage arc and carbon
- Darling, David, "Ball lightning". The Encyclopedia of Astrobiology, Astronomy, and Spaceflight.
- Shelto, J. D., "Eddy Current Model of Ball Lightning". Fruita, Colorado. January 13, 2004.
- Straight Dope: Does ball lightning really exist?
- Ball lightning properties
- Open Directory Project: Ball Lightning
- Ball Lightning as a Stable Toroid
- The Physical Theory of Ball Lightning
- Experimental modelling of ball lightning at balllightning.narod.ru.
- Step by step guide to building your own ball lightning using a household microwave at http://jlnlabs.online.fr/plasma/gmr/index.htm.
- Ball Lightning musings by Stephen Goodfellow. Some collected eye witness accounts and an attempted experiment.