The true brightness of an object is called its

A. luminosity.

B. intensity.

C. magnitude.

D. viscosity.

The true brightness of an object is called its luminosity. It is the total amount of energy emitted by bright or meteorological objects over a period of time. It has the SI unit of joules per second or watts. So the answer is letter A. Intensity is the measure of how strong the substance or object is when it projects something. Magnitude is a measure of how great is the size the object produces. Viscosity is the measure of flow of a substance.