The word ‘moon’ can function as both a common noun and a proper noun, depending on the context in which it is used.
When we refer to the moon in general terms, such as in the phrase ‘the moon is bright tonight,’ it acts as a common noun. This is because we are talking about the moon as a celestial body without specifying which one.
However, when we use ‘Moon’ to refer to Earth’s moon in a way that highlights its uniqueness, such as ‘The Moon orbits the Earth,’ it is considered a proper noun. In this context, it is treated as a specific entity, distinct from other moons found in the universe.
In summary, ‘moon’ is usually a common noun, but when it is capitalized to ‘Moon,’ it becomes a proper noun when discussing Earth’s only natural satellite.