* Sun: A star, the center of our solar system.

* Planet: A large celestial body that orbits a star. Earth is a planet orbiting the Sun.

* Moon: A natural satellite that orbits a planet. Our Moon orbits Earth.

* Galaxy: A vast collection of stars, gas, dust, and planets held together by gravity. Our solar system is located in the Milky Way galaxy.

So, the order from smallest to largest is:

1. Moon (orbits a planet)

2. Planet (orbits a star)

3. Sun (a star)

4. Galaxy (contains many stars, planets, and solar systems)