* Definition of a planet: The International Astronomical Union (IAU) defines a planet as a celestial body that:

* orbits the Sun

* 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.

* The Moon's status: The Moon orbits the Earth, not the Sun. It also doesn't clear its neighborhood – it shares its orbit with other objects.

Historical perspective:

While the Moon wasn't classified as a planet, ancient civilizations did often view it as a separate celestial body with its own importance. However, as our understanding of the solar system developed, its true nature as a satellite became clear.