What is lightning?

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Why Lightning Then Thunder

    A lightning flash and the clap of thunder that comes from it, happen at about the same time. Lightning is a giant electric spark and has kilometers long. Thunder is the noise made when the lightning causes the air to heat up and expand suddenly.

    We see the lightning first because light travels so fast. Thunder travels much more slowly and it takes the sound longer to get to our ears. One way to tell if a flash of lightning is far away or not is by counting the seconds before you hear the thunder. If it takes one second, the lightning and thunder are about three kilometers away. If they seem to happen together, you will know that the lightning is very close.

What is lightning?