Here's why:

* Moons are non-luminous objects: They do not produce their own light. They reflect light from their host star, which in our case is the Sun.

* Moons are not planets: The International Astronomical Union (IAU) defines a planet as a celestial body that:

* orbits a star

* has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape

* has cleared the neighborhood around its orbit

Moons do not meet the third criterion. They share their orbital space with other celestial bodies, unlike planets.

Therefore, moons are non-luminous objects that orbit planets, and they are not considered planets.