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, 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.
Scientists have proposed a number of hypotheses to explain reports of ball lightning over the centuries, but scientific data on ball lightning remain scarce. The presumption of its existence has depended on reported public sightings, which have produced inconsistent findings. Owing to the lack of reproducible data, the existence of ball lightning as a distinct physical phenomenon remains unproven.
Historical accounts
Ball lightning is a possible source of legends that describe luminous balls, such as the mythological Anchimayen from Argentinean and Chilean Mapuche culture.
According to statistical investigations in 1960, ball lightning had been seen by 5% of the population of the Earth. Another study analyzed reports of 10,000 cases.
Gervase of Canterbury
The chronicle of Gervase of Canterbury, an English monk, contains what is possibly the earliest known reference to ball lightning, dated 7 June 1195. He states, "A marvellous sign descended near London", consisting of a dense and dark cloud, emitting a white substance that grew into a spherical shape under the cloud, from which a fiery globe fell towards the river.
Physicist Emeritus Professor Brian Tanner and historian Giles Gasper of Durham University identified the chronicle entry as probably describing ball lightning, and noted its similarity to other accounts:
Great Thunderstorm of Widecombe-in-the-Moor
One early account reports on the Great Thunderstorm at a church in Widecombe-in-the-Moor, Devon, in England, on 21 October 1638. Four people died and approximately 60 suffered injuries during a severe storm. Witnesses described an ball of fire striking and entering the church, nearly destroying it. Large stones from the church walls were hurled onto the ground and through large wooden beams. The ball of fire allegedly smashed the pews and many windows, and filled the church with a foul sulphurous odour and dark, thick smoke.
The ball of fire reportedly divided into two segments, one exiting through a window by smashing it open, the other disappearing somewhere inside the church. Because of the fire and sulphur smell, contemporaries explained the ball of fire as "the devil" or as the "flames of hell". Later, some blamed the entire incident on two people who had been playing cards in the pews during the sermon, thereby incurring God's wrath.
The sloop Catherine and Mary
In December 1726, a number of British newspapers printed an extract of a letter from John Howell of the sloop Catherine and Mary:
HMS Montague
One particularly large example was reported "on the authority of Dr. Gregory" in 1749:
Admiral Chambers on board the Montague, 4 November 1749, was taking an observation just before noon...he observed a large ball of blue fire about distant from them. They immediately lowered their topsails, but it came up so fast upon them, that, before they could raise the main tack, they observed the ball rise almost perpendicularly, and not above from the main chains when it went off with an explosion, as great as if a hundred cannons had been discharged at the same time, leaving behind it a strong sulphurous smell. By this explosion the main top-mast was shattered into pieces and the main mast went down to the keel.
Five men were knocked down and one of them very bruised. Just before the explosion, the ball seemed to be the size of a large mill-stone.