Earth is a small planet in the vastness of space. It is one of eight planets that travel through space around the sun. The sun is a star—one of billions of stars that make up a galaxy called the Milky Way.

The Milky Way and as many as 100 billion other galaxies make up the universe.

The planet Earth is only a tiny part of the universe, but it is the home of human beings and, in fact, all known life in the universe. Animals, plants, and other organisms live almost everywhere on Earth's surface. They can live on Earth because it is just the right distance from the sun. Most living things need the sun's warmth and light for life. If Earth were too close to the sun, it would be too hot for living things. If Earth were too far from the sun, it would be too cold for anything to live. Living things also must have water to live. Earth has plenty. Water covers most of Earth's surface.