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A Cloud Forms skydiver jumps out of a plane and falls


toward the ground. She quickly passes into a cloud. It’s nothing like a white, puff y pillow. Instead, a thick, white fog surrounds her. Small drops of cold water drench her. She worries that she might slam into some hail, or winds might toss her around. It might seem odd to think of clouds this


way. Aſt er all, you might think of them as giant puff s of cotton or tuſt s of tissue. Some clouds do look like that, but others don’t. In fact, some clouds are really odd looking and form in unique ways. Join me as I travel the world, searching for them.


Fascinated by Clouds


High, wispy clouds race across the sky, waving like the tails of horses. Big, puff y white clouds graze the sky like herds of giant sheep. Dark, powerful storm clouds boil up with an energy all their own. T ey growl with thunder and zap with lightning bolts. I’ve seen clouds that shine a ghostly blue


at night. I’ve watched some clouds curl like breaking waves, and others roll toward me faster than a speeding truck. T e more clouds I see, the more fascinated I become. It makes me want to understand how they form and why they come in so many shapes and sizes. Here’s some of what I’ve learned. Clouds may look diff erent, but they all form


in about the same way. It’s all in how Earth’s major systems—water, land, and air—interact. To see how this happens, let’s tour some of my favorite clouds.


The first thing to know is that all clouds are made of a lot of water or ice. A fluff y, white cloud, for instance, is made up of so much water that it can weigh 200 tons. T at’s as heavy as 80 elephants! T at water is part of the hydrosphere, or


the part of Earth that is made of water. As the sun shines on rivers, lakes, and oceans, it warms the water. Some water gets so warm that it evaporates, changing into a gas called water vapor. T e vapor rises into the atmosphere, or the air that surrounds Earth. As the vapor rises, it expands. T at causes


it to cool. As the vapor cools, it turns back into drops of water. It forms droplets smaller than the period at the end of this sentence. T e droplets cling to tiny specks of dust floating in the air. When hundreds of millions of droplets collect in an area, they form a cloud.


3 The water droplets cling to dust in the atmosphere,


forming clouds.


4 Clouds release rain, sleet, snow, or ice.


18


Fun Fact


At any moment, clouds cover 70 percent


of Earth.


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