Lightning is a giant spark of electricity that jumps through the sky during a thunderstorm. It’s one of the most powerful forces in nature, heating the air around it to about 50,000 degrees Fahrenheit, which is five times hotter than the surface of the sun. Around the world, lightning flashes about 100 times every single second.
How Lightning Forms Inside a Cloud
Lightning starts inside tall storm clouds called cumulonimbus clouds. These clouds are like giant weather engines. Strong winds inside them push tiny water droplets upward, sometimes to heights of 35,000 to 70,000 feet. That’s so high the droplets freeze into ice. At the same time, heavier chunks of ice and hail get pulled downward.
Here’s where things get interesting. As the rising ice bits and falling hail bump into each other, they swap tiny particles called electrons. Think of it like rubbing a balloon on your hair and creating static. The falling pieces collect extra electrons and carry a negative charge to the bottom of the cloud. The rising pieces lose electrons and carry a positive charge to the top. Eventually the difference between the top and bottom of the cloud becomes so huge that electricity has to jump to balance things out. That jump is lightning.
Why Lightning Zigzags
If you’ve ever looked closely at a lightning bolt, you’ve noticed it doesn’t travel in a straight line. It zigzags downward in short steps, roughly 50 yards at a time, branching out like the roots of a tree. Scientists call this a “stepped leader.” It’s searching for the shortest, easiest path to the ground. Once it connects, a massive burst of electricity shoots back up through that channel almost instantly, creating the bright flash you see.
Where Lightning Can Go
Most lightning never touches the ground at all. For every bolt that strikes the earth, about five to ten bolts stay inside the cloud or jump between clouds. These are called intra-cloud flashes. Some bolts even reach out into the open air around a storm without hitting anything. The cloud-to-ground bolts are the ones people notice most because they’re the brightest and the most dangerous.
What Causes Thunder
Thunder is lightning’s sound effect, and the science behind it is wild. When a lightning bolt fires, it heats the air in its path to around 54,000°F in a tiny fraction of a second. That superheated air expands so fast it basically explodes outward, compressing the air in front of it and creating a shock wave. That shock wave is what you hear as thunder. It’s the same idea as a sonic boom from a jet, just caused by heat instead of speed.
You can use thunder to figure out how far away a storm is. Light travels almost instantly, but sound is much slower, covering about one mile every five seconds. So after you see a flash, count the seconds until you hear thunder, then divide by five. If you count to 15, the lightning was about three miles away. If you count to five, it was only one mile away. If you hear thunder at almost the same moment you see the flash, it’s extremely close.
Wild Lightning Facts
Lightning can do some truly jaw-dropping things. The longest single bolt ever recorded stretched 515 miles, from eastern Texas all the way to near Kansas City, Missouri. That’s roughly the distance you’d drive from Dallas to Little Rock and then some. NOAA’s weather satellite captured that megaflash on October 22, 2017.
Scientists have also discovered bizarre types of lightning that happen high above storms, near the edge of space. Sprites are reddish bursts of electricity shaped like jellyfish that appear about 50 miles above the ground. They last less than a second. Gigantic jets are even more dramatic, shooting upward from cloud tops into the ionosphere, traveling 50 to 56 miles straight up. And ball lightning, one of the rarest forms, appears as a glowing orb (anywhere from golf ball to beach ball sized) that can float through the air for several seconds. It can be white, yellow, red, orange, purple, or green, and scientists are still working out exactly how it forms.
How Lightning Rods Protect Buildings
You might have seen a metal rod sticking up from the top of a tall building or a barn. That’s a lightning rod, and it doesn’t actually prevent lightning from striking. Instead, it gives lightning an easy path to follow. The rod connects to a thick metal cable that runs down the side of the building and into the ground. When lightning hits the rod, the electricity travels through the cable and spreads safely into the earth instead of ripping through the building’s walls, wiring, or roof.
Staying Safe During a Storm
A good rule to remember is the 30/30 rule. When you see a flash of lightning, start counting. If you hear thunder before you reach 30, you need to get inside a solid building right away. That count of 30 means the storm is about six miles away, close enough to be dangerous. After the storm seems to pass, wait at least 30 minutes after the last rumble of thunder before going back outside.
Being inside doesn’t mean you can ignore the storm completely. Lightning can send electrical currents through plumbing and wiring, so stay away from sinks, bathtubs, showers, and open windows during a storm. Swimming is especially dangerous because water conducts electricity, so pools, lakes, and oceans are all off-limits until the storm is well past. The simplest safety motto works best: when thunder roars, go indoors.