Each object in the sky is attached to a sphere and moves around Earth as that sphere rotates. Geocentric means “Earth-centered.” In the geocentric model, the sky, or heavens, are a set of spheres layered on top of one another.

This view is called the geocentric model of the universe. The ancient Greeks believed that Earth was at the center of the universe, as shown in Figure below. Since then, scientists have discovered two more planets, many other solar-system objects and even planets found outside our solar system. The ancient Greeks identified five of the planets and for many centuries they were the only planets known.

Humans’ view of the solar system has evolved as technology and scientific knowledge have increased. Name the planets, and describe their motion around the sun.Describe historical views of the solar system.