A bike, a tree, a cloud, an ocean—any object you can name—it's all made of matter. Even YOU are made of matter. Matter is anything that takes up space and has mass. All matter is made of tiny particles called atoms. The only difference between different kinds of matter—whether you're talking about bugs, rocks, humans, or stars—is the way their atoms fit together.

Image credits: main image, © AMNH/Eric Hamilton.