To understand lightning, start small—really small. Everything is made up of teeny-tiny atoms. And atoms have three even tinier parts: protons, electrons, and neutrons. You can imagine protons with a plus sign on them, because protons have a positive electrical charge. (Remember this by thinking of three p words: proton, positive, and plus.) Neutrons are neutral. We don’t have to worry about them much when we’re talking about lightning. But electrons are negative. You can imagine each electron wearing a minus sign.

Normally, atoms have the same amount of protons and electrons. These neutral atoms just go along minding their own business. But other atoms have more protons than electrons. These have a positive charge. And some atoms have more electrons than protons, which gives them a negative charge. With electricity—just like with people—opposites attract. Positive and negative charges like each other. They want to be together.

So what does all this have to do with lightning? Well . . .

Clouds look like big, dry, puffy masses. But really they are made up of tiny water droplets. The clouds form when Earth’s warmth carries water up into cooler air. Then the moisture droplets get cold. They turn into ice. But ice is heavy! It can’t just float around. It falls. As it does, CRASH! It hits moisture droplets on their way up. Electrons get knocked loose. Neutral atoms are thrown out of balance. The falling bits take on a negative charge. You can find all these negative atoms at the bottom of a cloud.

Now the real drama starts! Positive charges on the ground want to get to the negative charges in the cloud. They crowd upward into trees, towers, and tall buildings. In a flash, the positive and negative charges make a white-hot path of energy to each other. That path is lightning.