Magnitude is the common term, the luminosity of a star is also used.
Brightness of stars (apparent and absolute magnitude) is measured by convention, taking an another star as a standard.
intrinsic magnitude
An apparent brightness is the brightness of a star as measured by an observer.
Magnitude refers to the brightness of a star. There are two main types: apparent magnitude, which is how bright a star appears from Earth, and absolute magnitude, which measures a star's intrinsic brightness.
Three physical factors that determine a star's brightness are its temperature (hotter stars are brighter), size (larger stars are generally brighter), and distance from Earth (the closer a star is, the brighter it appears).
Brightness of stars (apparent and absolute magnitude) is measured by convention, taking an another star as a standard.
Magnitude
the brightness of a star
The measure of a star's brightness is its magnitude. A star's brightness as it appears from Earth is called its Apparent Magnitude.Star's brightness is measured by there magnitude.
The brightness of a star is called its luminosity. This refers to the total amount of energy a star emits per second, taking into account its brightness across all wavelengths of light.
intrinsic magnitude
Scientists use the term magnitude to describe a star's brightness.
intrinsic magnitude
photographs use to measure the brightness of a star
Normally you would observe the star's brightness, not its apparent diameter.The star's apparent brightness ("apparent magnitude") depends on its real brightness ("absolute magnitude"), and on the distance. Similarly, the star's apparent angular diameter (which is VERY hard to measure) would depend on its actual diameter, and on the distance.
The brightness as seen from Earth is called the "apparent magnitude".The real brightness (defined as the apparent brightness, as seen from a standard distance) is called the "absolute magnitude".
There is no purpose of a star's brightness. They just exist and shine.