Ball lightning

You've all seen lightning - there's nothing quite as good as being in the middle of a decent summer thunderstorm. But have you seen ball lightning?

Ball lightning takes the form of a glowing, floating object often the size and shape of a basketball. 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. Sometimes the discharge is described as being attracted to a certain object, and sometimes as moving randomly. After several seconds the discharge reportedly leaves, disperses, is absorbed into something, or, rarely, vanishes in an explosion.

Ordinary ball lightning is probably "normal plasma." It is the kind of ball lightning produced in the laboratory. It spontaneously appears in the open-air, closed rooms, aircraft at altitude, and was seen in at least one submarine. It appears before, during or after lightning. About 5% are seen in clear weather.

Then you get extreme ball lightning:
• it glows in air;
• it originates from nothing visible;
• it lasts between 10 and 1200 seconds;
• it floats at about 1 meter/second;
• it is lethal or potentially lethal;
• it causes significant damage;
• it contains energy estimated at 100,000 to 1 billion Joules, far in excess of the energy density attributable to chemicals or electrostatics;
• it penetrates walls, glass and metal, generally without leaving a hole;
• it induces large currents but is in radial force equilibrium;
• it leaves black streaks on corpses without the spasm of electrocution;
• it can excavate tons of earth.

I saw it once as a kid - two balls of white light travelling parallel to the ground, following the contours of the hills. Didn't know what it was at the time of course - and my geography teacher thought I was nuts.