By Jessica Handwerker

Many people have seen flashes of lightning and heard claps of thunder from a thunderstorm, but have you ever thought about what causes lightning and why light can cause the sound of thunder?

Lightning is a current of electricity traveling from a cloud down to the ground. Clouds are made up of many water particles, and some freeze into ice because of the cold temperatures high up in the sky. These ice particles are so light that they can move around in the air, and sometimes bump into each other. When this happens positive and negative charges get knocked off of the ice particles and are released into the cloud. Over time, the top of the cloud becomes positively charged and the bottom of the cloud becomes negatively charged. The ground below the cloud has a lot of positive charges, which are attracted to the negative charges at the bottom of the cloud. Since opposite charges attract, the positive charges in the ground want to get as close as they can to the negative charges in the cloud, so they travel upward. For example, they might go to the top of a tree or a building since this is closer to the cloud than the ground. Eventually, the cloud gets so many negative charges at its base that a stream of negative charged particles (called electrons) go from the cloud to the positive charges on the ground forming a lightning bolt. Once the lightning bolt hits ground, the positive charges in the ground can travel up to the cloud, making it so the cloud has a more even balance of positive and negative charges in its base. If there are trees or buildings close to the thunderstorm, lightning is more likely to strike these since the positive charges try and get as close to the cloud as they can. This is why it is important to get under a shelter in a thunder storm. If you are close to or under something that is taller than you, the positive charges will to to the top of that object and make it more likely for the lightning to strike that instead of you. However it is still not a good idea to stand right next to a tree or flag pole during a thunder storm since that will attract the lightning, and the electricity can travel through the ground after a lightning strike. The safest place to be during a thunderstorm is inside a building, or in a car if you can’t get inside.

When lightning strikes, it creates a lot of heat. In fact, lightning can heat the air around it to 54,000 degrees Fahrenheit, which is about 4 times hotter than the surface of the sun! Heat gives the air energy, which causes it to expand really quickly and creates a shock wave. The initial boom of thunder is caused by the expansion of the heated air, and the rumbles after are caused by other air particles moving to the space that used to be filled by the heated air. You can see lightning before you hear thunder, because light travels faster than sound. One way to tell how far away lightning is from you is by counting how long it takes to hear thunder after you see a bolt of lightning. Sound takes about 5 seconds to travel a mile, so the lightning is about a mile away for every 5 seconds that passes.