The correct term that represents the brightness of a celestial object measured from Earth is Apparent magnitude.
- Absolute brightness (or absolute magnitude) refers to the intrinsic brightness of a celestial object, as it would be seen at a standard distance of 10 parsecs (about 32.6 light-years) from the observer.
- Luminosity is the total amount of energy emitted by a star or celestial object per unit of time, regardless of distance.
- Proto-star is a stage in the formation of a star and not related to brightness measurements.
So, the answer is Apparent magnitude.