 Look! It's a cloud! But what type of cloud is it? Clouds are given different names depending on their shape and their height or altitude in the atmosphere. Low in the atmosphere, you'll find cumulus clouds. These grow vertically so they can become higher clouds over time. They look like floating cotton balls with sharp outlines. They're usually flat on the lower side and puffier on the top. Stratus clouds are also found low in the atmosphere. In fact, sometimes they touch the ground and are called fog. They are uniform gray in color and cover most of the sky. Stratocumulus clouds look like a combination of stratus and cumulus clouds. They have puffy cumulus shapes that are elongate and uniform, like stratus clouds. Higher in the atmosphere, you can find alto-cumulus clouds. Like cumulus, these look puffy like cotton, but they're higher in the sky so they appear smaller. Extend your arm out towards the sky. If the little puffs of cloud are about as wide as your thumb, then the clouds are alto-cumulus instead of cumulus. Alto-cumulus clouds can also form ridges in the sky that look like waves or the scales of fish. Alto-stratus clouds are also found at mid-levels. They are usually bluish gray in color and cover most of the sky. They might be thin enough that you can see the sun or moon shine through. At high altitudes, you'll find serocumulus clouds, small rounded puffs, smaller than the puffs of alto-cumulus clouds. Extend your arm towards the sky and compare the size of the puffs to your smallest finger. If the puffs of cloud are about the same size or smaller than their serocumulus. You'll also find serostratus clouds at high altitudes. Like other stratus clouds, these form a thin sheet over the sky. And there are also serous clouds at high levels. These look like wispy white streamers. A couple of the cloud types are known to make rain or snow. Cumulus nimbus clouds are responsible for thunderstorms. They form when cumulus or alto-cumulus clouds grow over time. Nimbus stratus clouds are dark gray and cause the type of rainstorms that's calm and gloomy, where soft rain falls without wind or lightning. There are also human-made clouds called contrails. These are clouds that form from water vapor released by airplanes. So head outside and identify the cloud types that you see in the sky.