On 21 October 1638, during a Sunday afternoon service, a violent thunderstorm struck the village of Widecombe-in-the-Moor in Devon, England. Contemporary accounts describe the church darkening, then a great ball of fire bursting in through a window. Parts of the church were damaged, several people were killed and many injured, and the congregation was left in terror and confusion.

The villagers blamed the Devil. Modern writers often point to it as one of the earliest detailed descriptions of something called ball lightning.

What people see

Accounts of ball lightning are remarkably consistent. During or just after a thunderstorm, a glowing sphere appears, usually somewhere between the size of a golf ball and a football, though some are reported to be much bigger. It might be white, yellow, orange, red or blue. It drifts or rolls through the air, often horizontally, for a few seconds — rarely more than ten or so — and then disappears, sometimes silently, sometimes with a bang.

People have reported ball lightning floating into houses through closed windows, travelling down chimneys and even moving along the aisle of an aeroplane in flight.

Why scientists doubted it

The trouble was evidence. Ball lightning is rare, unpredictable and brief. Almost all the information came from eyewitnesses who had been frightened by a thunderstorm and saw something for a few seconds. Photographs were rare and often unconvincing.

Some researchers suggested many sightings could be optical illusions, after-images from bright lightning flashes, or misidentified phenomena. And no one could easily make it in a laboratory.

Caught by accident

In July 2012, a team of Chinese scientists was studying ordinary lightning on the Qinghai part of the Tibetan Plateau, using high-speed cameras and spectrographs, which split light into its colours to reveal what's glowing.

Lightning struck the ground about 900 metres away. Then, to their astonishment, a glowing ball rose from the spot where it had hit and drifted along for more than a second before fading. Their instruments recorded it.

When they analysed the light, they found the signatures of silicon, iron and calcium — elements found in soil. They published their results in 2014. It was the first time the spectrum of a natural ball lightning had been recorded.

Theories

Still a mystery

Ball lightning is no longer seen as a myth, but it is still not fully understood. One recording, however exciting, doesn't explain every report. Researchers hope that the growing number of high-speed cameras, phone cameras and lightning-monitoring stations will eventually capture more examples.

Making it in the lab

Because natural ball lightning is so hard to catch, physicists have tried to create glowing balls on purpose. In 2007, researchers in Brazil vaporised silicon wafers with an electric arc and produced luminous balls the size of ping-pong balls. They drifted and glowed for several seconds, which is far longer than an ordinary spark lasts.

Other teams have made long-lived glowing blobs by discharging high voltages into salty water, or by focusing microwaves into small regions of air. None of these lab experiments perfectly matches every eyewitness description. But they show that glowing, floating balls of energy that last for seconds are physically possible, which is something many scientists once doubted.

Pilots and aeroplanes

Some of the strangest reports come from aircraft. Pilots and passengers have described glowing balls appearing near the cockpit or drifting down the cabin during storms. In 1963, the physicist Roger Jennison reported seeing a glowing sphere about 20 centimetres across float down the aisle of an airliner he was travelling in during a thunderstorm. Because he was a trained scientist, his account was taken seriously. It helped persuade others that the phenomenon was worth studying.