Lightning is a giant electrical spark in the sky. Most of the lightning people see takes place between a cloud and the ground. But lightning also occurs within a cloud, between a cloud and the air, and between two clouds. When lightning occurs in the atmosphere, its electrical energy scatters in the air. This energy may damage airplanes traveling through it, but it does not cause harm on the ground. But lightning that strikes the earth may kill people or cause fire.
             Lightning that strikes the earth consists of one or more electrical discharges called strokes. The bright light that we see in a flash of lightning is called a return stroke. Return strokes travel at about the speed of light, which is 186,282 miles per second. They discharge about 100 million bolts of electricity and heat the air in their paths to over 60,000 °F Air heated by return strokes expands quickly, producing a wave of pressure called thunder.
             Flashes of lightning differ in length. A flash between a cloud and the ground can be up to 9 miles long. A flash that travels through clouds side by side can be more than 90 miles long.
             Everything around us is made up of atoms. Although atoms are usually neutral, they can become positive or negative if they lose or gain electrons. Positive and negative charges are attracted to one another. So when they move through air toward one another, they form an electric current that causes a spark. Lightning is the spark that you get from the fast movement of electrically charged particles within a thundercloud or between a cloud and the ground, the air, or another cloud.
             Lightning occurs in a variety of different forms. A single flash of lightning varies in appearance. The major forms of lightning include forked lightning, streak lightning, ribbon lightning, and bead, or chain, lightning. Forked is a flash in which a lot of branches of a stroke are visible. Streak lig
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