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This map provided by the National Aeronautics and Space Administration shows the uneven distribution of lightning strikes across the planet. Units are in flashes per square kilometer per year. PD-GOV.

There are few common displays of nature that are more dramatic than lightning — happening in an instant, a lightning strike is hotter than the surface of the sun and creates a sound that sometimes can be heard as far away as 25 miles or 40 kilometers. It’s no wonder that since ancient times lightning has been associated with the gods, and that even today being caught in a thunderstorm can be a frightening experience.

Surprisingly, scientists are still learning precisely about how lightning is formed. Although researchers don’t know all the details of how, a lightning strike begins as part of the everyday cycle of water evaporation and condensation. Water on the Earth’s surface is warmed by the sun, causing it to evaporate, and the water molecules are eventually lifted high in the atmosphere, where they eventually condense to form clouds, which are nothing more than collections of tiny water droplets. As the water molecules rise, they collide with other molecules. In that process, some of the electrons — subatomic parties with a negative charge — are knocked off the rising water molecules. The result is that the rising water molecules are ionized, meaning that without all their electrons they have a positive charge, while the electrons left behind have a negative charge. The result is a huge disparity in charges — a positive charge on top of the cloud, a negative charge far below.

Under certain conditions, the differences in charges becomes so great, making the sky something like a huge battery — the positive “terminal” at top, the negative at the bottom. Nature doesn’t like such a great disparity in charges, and eventually under the right conditions the difference can become so great that the surplus of elections “breaks through” the air, forming what amounts to a gigantic spark.

This all happens quite quickly — the electrical bolt travels at about 60,000 miles or 100,000 kilometers per second. And that electric current creates so much heat — it is around 50,000 degrees Fahrenheit or 30,000 degrees Celsius — that it causes the area immediately around it to expand with explosive force, which we hear as thunder.

Most thunder strikes take place within clouds, but they can also hit the ground and cause considerable damage. About 100 lightning strikes occur each second somewhere on the planet. Lightning storms are most common in central Africa, but they occur over all the Earth’s land masses other than Antarctica.