Ball lightning is a rare and unexplained phenomenon described as luminescent, spherical objects that vary from pea-sized to several meters in diameter. Though usually associated with thunderstorms,[1] the observed phenomenon is reported to last considerably longer than the split-second flash of a lightning bolt, and is a phenomenon distinct from St. Elmo's fire.
Some 19th-century reports describe balls that eventually explode and leave behind an odor of sulfur. Descriptions of ball lightning appear in a variety of accounts over the centuries and have received attention from scientists. An optical spectrum of what appears to have been a ball lightning event was published in January 2014 and included a video at high frame rate. Laboratory experiments have produced effects that are visually similar to reports of ball lightning, but how these relate to the supposed phenomenon remains unclear.
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, altitudes of 300 m (1,000 feet) and higher, and during thunderstorms and 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, being absorbed 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 (0.4–40 inches), most commonly 10–20 cm (4–8 inches)
Their brightness corresponds to roughly that of a domestic lamp, so they can be seen clearly in daylight
A wide range of colors has been observed, with red, orange, and yellow being the most common
The lifetime of each event is from one second to over a minute with the brightness remaining fairly constant during that time
They tend to move at a few meters per second, most often in a horizontal direction, 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 sulphur, or nitrogen oxides are often reported
