Lucille and Sal Pereschino woke around midnight when the air conditioner in their Johnston, Rhode Island, home shut off. A summer lightning storm had cut their electricity, the couple realized; but they saw a light coming from the kitchen. They crept down the hall to investigate.
What they saw looked like some sort of science fiction nightmare: Bouncing on the linoleum kitchen floor were tiny orange fireballs smaller than a fingertip. Then they vanished. “We were petrified,” Lucille told a reporter after the incident in 1972. They sold the house.
What the Pereschinos saw is known as ball lightning—small, apparently harmless fireballs that typically come popping out of wall sockets, zooming through airline windows, zipping down chimneys. They bounce around, sparkling, and then disappear, often with a loud pop. “Many people don’t believe in it,” says Massachusetts Institute of Technology meteorologist Earle Williams; but there are so many reliable eyewitness reports of ball lightning, he said, “you almost have to believe it’s a real phenomenon.”
Certainly, lightning experts have seen lightning do even stranger things: like light up the wings of aircraft, the masts of ships or even the fingertips of scientists with an eerie, sizzling, flameshaped green glow. This is known as St. Elmo’s fire—a phenomenon so weird that Mediterranean sailors long believed the ghostly light was the embodiment of a third-century saint come to protect them from the storm.
Lightning can make a tree branch explode like a firecracker, blow a person’s shoes and socks off his feet or make him leap into the air like a marionette. Lightning makes the impossible possible; and summer, with its fast-rising, anvil-shaped, dark thunderclouds, gives birth to most of North America’s lightning storms.
When you see these clouds gathering, go inside and watch the show. “Nature’s most beautiful fireworks,” is how Martin Uman, professor of electrical engineering at the University of Florida in Gainesville, describes these bolts from the blue. Watching a thunderstorm affords a look into the inner workings of a cloud that is generating the force of a nuclear power plant. You’ll be witnessing an event that virtually defines the supernatural: lightning is nature at the height of its power, a heavenly display of seemingly infinite energy and light.
A single flash of lightning shines as brightly as a million one hundred-watt light bulbs, heats the air hotter than the surface of the sun and carries enough electricity to run twenty thousand toaster ovens. No wonder cultures around the world have interpreted lightning and thunder as direct evidence of gods at work.
Lightning can be deadly. It kills about eighty people in the United States each year, most of whom are outside. Golfers, the tallest things on a flat fairway, are frequent victims: wearing metal cleats and carrying metal clubs, their bodies become ideal conductors of electricity. If you are indoors, talking on the telephone or using an electrical appliance during a storm can also make you a target.
Yet for all its power, lightning is surprisingly benign. Although at this moment, eighteen hundred storms around the world are producing a hundred lightning flashes per second, three-quarters of all lightning never touches the ground. Instead, it flashes between clouds or within the cloud where it was born. (This often shows up as “heat lightning” or “sheet lightning”—a flash hidden from direct view that is seen reflected from clouds.) Lightning does not kill everyone it strikes; 66 percent, in fact, recover instantly without a wound or scar.
Lightning, like the gods, can be beneficent as well as terrifying. It prunes forests, taking out the tallest trees so younger ones can grow. Were it not for lightning, says Uman, Florida’s forests would have no oaks, for the tall pines would shade them all out. Lightning also fertilizes the soil. Purdue University agronomist David Mengle credits 1992’s copious thunderbolts for Indiana’s record growing season that summer: each lightning strike transforms hydrogen and nitrogen into ammonia, a natural fertilizer.
Lightning forms in a thundercloud when positive and negative charges become separated—though why the charges separate no one really knows. The positive charges stay near the top of the towering, flat-topped cloud, while the negative charges accumulate near the bottom. When the cloud’s bottom charge becomes strong enough, a flow of electricity zigzags down toward the ground. This flow of energy is not the lightning stroke, however. Barely visible and lasting only a microsecond, this is called a stepped leader. Because opposites attract, positive charges from the ground come racing toward the negatively charged stepped leader. The region of positive charge moves up through any conducting objects in the area—including trees, electrical wires, and people. It is this brilliant return stroke—coming from the Earth to the sky—that closes the electrical circuit, causing the celestial fireworks of lightning.
The flash appears to be going down because it retraces the downward-forking path of the stepped leader. What seems to be a single flickering flash is actually often a dozen or more strokes, each one only ten-thousandths of a second long, in the same path.
After the flash, you hear the crack and rumble of thunder. The closer the lightning, the more rapid the report of the thunder, the shock wave of air exploding in the fifty thousand-degreeFahrenheit heat of the flash. By listening to the thunder, you can estimate how far away the lightning is. (Sound travels much slower than light: in the one second it takes sound to travel four city blocks, light can make it seven times around the world.) Count the seconds between the time you see the flash and the time you hear the thunder. Each second accounts for about a thousand feet between you and the flash. In five seconds, the sound will have traveled a mile.
Thunder’s rumble can also help you measure the length of the lightning channel. The sound will continue all along the lightning’s path; if the rumbles continue for twenty seconds, for instance, you will know the lightning bolt was at least four miles long.
The best time to watch a thunderstorm is at dusk, when it is light enough to see the outlines of the clouds yet dark enough to appreciate the lightning. In bright daylight, without special optical detectors, we miss 90 percent of the lightning flashes a storm has to offer, Uman says. Look for the earliest flickers near the top of the thundercloud; then watch the flashes move deeper and deeper into the cloud. If you have a choice of thunderclouds to watch, pick the tallest one, he advises. A cloud twice as deep will produce thirty times more lightning.
The ancients watched lightning carefully, reading in its strikes good luck and bad. One fellow in Maine claims that lightning definitely brought him good luck: On a June day when he was sixtytwo years old, his hearing, his sight—and even his hair—returned after he was struck by lightning.