* Definition: A moon is a natural satellite that orbits a planet.

* Function: The sun is a star, a massive ball of hot gas that produces its own light and heat through nuclear fusion. It's the center of our solar system and provides the light and warmth that sustains life on Earth.

* Orbit: Moons orbit planets, while planets orbit stars. The Earth orbits the sun.

So, while both the sun and moon are celestial bodies, they have very different functions and roles in our solar system.