Characteristics
Descriptions of ball lightning vary widely. It has been described as moving up and down, sideways or in unpredictable trajectories, hovering and moving with or against the wind; attracted to, unaffected by, or repelled from buildings, people, cars and other objects. Some accounts describe it as moving through solid masses of wood or metal without effect, while others describe it as destructive and melting or burning those substances. Its appearance has also been linked to power lines as well as during thunderstorms and also calm weather. Ball lightning has been described as transparent, translucent, multicolored, evenly lit, radiating flames, filaments or sparks, with shapes that vary between spheres, ovals, tear-drops, rods, or disks.
Ball lightning is often erroneously identified as St. Elmo's fire. They are separate and distinct phenomena.
The balls have been reported to disperse in many different ways, such as suddenly vanishing, gradually dissipating, absorption into an object, "popping," exploding loudly, or even exploding with force, which is sometimes reported as damaging. Accounts also vary on their alleged danger to humans, from lethal to harmless.
A review of the available literature published in 1972 identified the properties of a “typical” ball lightning, whilst cautioning against over-reliance on eye-witness accounts:
- They frequently appear almost simultaneously with cloud-to-ground lightning discharge
- They are generally spherical or pear-shaped with fuzzy edges
- Their diameters range from 1–100 cm, most commonly 10–20 cm
- Their brightness corresponds to roughly that of a domestic lamp, so they can be seen clearly in daylight
- A wide range of colours has been observed, red, orange and yellow being the most common.
- The lifetime of each event is from 1 second to over a minute with the brightness remaining fairly constant during that time
- They tend to move, most often in a horizontal direction at a few metres per second, but may also move vertically, remain stationary or wander erratically.
- Many are described as having rotational motion
- It is rare that observers report the sensation of heat, although in some cases the disappearance of the ball is accompanied by the liberation of heat
- Some display an affinity for metal objects and may move along conductors such as wires or metal fences
- Some appear within buildings passing through closed doors and windows
- Some have appeared within metal aircraft and have entered and left without causing damage
- The disappearance of a ball is generally rapid and may be either silent or explosive
- Odors resembling ozone, burning sulfur, or nitrogen oxides are often reported
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