A system is defined as a collection of interacting objects. The earth is a component of the solar system, which consists of the Sun and the celestial objects bound to it by gravity. Though Earth has relatively little interaction with the other planets, the Sun and the Earth's moon indeed do. The earth system receives receives energy from Sun, and gravitational attraction holds the Moon in an orbit around the Earth. The gravitational pull of the Moon on Earth's oceans creates tides as we'll see in Chapter 21. Let's begin an investigation of the earth system by examining the origin of the earth, its basic components, and its most important source of energy, the Sun.