Lightning is an electric charge or current. It can come from the clouds to the ground, from cloud to cloud, or from the ground to a cloud.

Lightning is a product of a planet’s atmosphere. Raindrops very high up in the sky turn to ice. When many small pieces of these frozen raindrops collide with each other in a thundercloud, they create an electrical charge. After some time, the entire cloud fills with an electrical charge. The negative charges (electrons) concentrate at the bottom of the cloud. The positive and neutral charges (protons) and neutral charges (neutrons) gather at the top of the cloud.

Negative charges and positive charges attract each other. Thunderclouds are full of electrical charges connecting with each other. These connections are visible as lightning.

On the ground beneath the cloud’s negative charges, positive charges build up. The positive charge on the ground concentrates around anything that protrudes, or sticks up—like trees, telephone poles, blades of grass, even people. The positive charges from these objects reach up higher into the sky. The negative charges in the thundercloud reach lower. Eventually, they touch. When they touch, lightning is created between the two charges.

This connection also creates thunder. Thunder is simply the noise lightning makes. The loud boom is caused by the heat of the lightning. When the air gets very, very hot, the heat makes the air explode. Since light travels much, much, faster than sound, you’ll see lightning before you hear thunder.

To figure out how far away a storm is, start counting seconds as soon as you see lightning. Stop when you hear thunder. The number you get divided by five is approximately the number of miles away the storm is. For example, if you see lightning and get to 10 before you hear thunder, the storm is about two miles (3.2 kilometers) away.

Lightning Safety

All thunderstorms and lightning storms are dangerous. Lightning is very, very hot—hotter than the surface of the sun. It can reach 28,000 degrees Celsius (50,000 degrees Fahrenheit). Lightning is more likely to strike objects that stick up off of the ground, including people. In the U.S., lightning kills an average of 58 people each year. That’s more deaths than are caused by tornadoes and hurricanes.

If you hear thunder or see lightning, you may be in danger. If you hear thunder, the storm is nearby. Go inside a safe place. Stay away from open areas, like fields, and tall objects, like trees or telephone poles. Stay away from anything metal, too, like chain-link fences, bikes, and metal shelters. Since water is a great conductor of electricity, you should get out of a pool if you’re swimming and stay away from puddles and any other water. If you’re in an area where there is no shelter, crouch low to the ground, but don’t lay down flat. If you’re in a group, stand at least five meters (15 feet) from anyone else.