Understanding Thunder and Lightning

From our earliest history to the present day, humans have experienced the flash of lightning and the crack of thunder as awesome natural forces.

There are countless legends explaining thunder and lightning – the Romans thought that thunder-bolts were the weapons of the god Jupiter while in Native American myth thunder is created by the thunderbird. In Medieval Europe, people believed that it was possible to avert lightning by ringing church bells.

There are also plenty of modern myths, the most famous being that ‘lightning never strikes twice’. This is clearly untrue, as the Empire State Building is hit about 20-25 times a year.

So what is lightning? The Ancient Greeks had several theories. Empedocles speculated that it was caused by sun-rays colliding with clouds. Aristotle thought that clouds emitted a ‘dry exhalation’ which burned and clashed with other clouds.

Many more ideas were put forward down the years, but it was the 18th-century scientist Benjamin Franklin who finally proved that lightning is electrical (according to the legend, he conducted a highly dangerous experiment involving a kite and an iron key).

We now know that lightning is a massive spark of static electricity which bridges the gap between the clouds and the land. Its heat expands the surrounding air, creating a compression wave which breaks the sound barrier and produces thunder.

Lightning is usually associated with rain-storms but it also occurs during blizzards, in the smoke which rises from forest fires, around volcanic clouds and nuclear fireballs, and even on other planets.

Lightning strikes the ground at 90,000 miles per second and is three times hotter than the surface of the sun. While each flash is approximately three miles long, it is only about a centimetre wide. At this very moment, about 2000 thunderstorms are occurring around the world, producing 6000 lightning-bolts a minute.

The lethal power of lightning must not be underestimated. On average, more people are killed by lightning in the USA every year than by hurricanes and tornadoes. While nine out of ten people do survive being hit, nearly 25% suffer long-term trauma. Some unfortunate people are hit more than once. The current record holder is Roy C. Sullivan, who was struck by lightning seven times.

The ‘Worst Lighting Strike Death Toll’ recorded in the Guinness Book of World Records occurred in 1963, when an airplane was hit on route from Baltimore to Philadelphia. The plane crashed, killing all 81 passengers.

When a thunder-storm approaches, the safest thing to do is take shelter in a building. As the National Lightning Safety Institute (NLSI) explains, if the space between the flash of lightning and the sound of thunder is thirty seconds or less, ‘the threat is imminent and the next strike may be at your location’.

The idea that you should seek cover beneath the branches of a tree is a dangerous myth – 18% of lightning victims are killed while standing under trees. Most people are hit either before or after the main downpour, which is why you should not leave cover until half-an-hour has passed since the last lightning-strike.

For more information, look up the NLSI’s Personal Lightning Safety Tips at lightningsafety.com.

Louisa Watson