Question

what is luminosity?
the amount of energy a star emits in a unit of time
the brightness of a star as seen from earth
the average temperature of a star during its life cycle
the degree of shift toward the red end of the spectrum

Explanation:

Luminosity is the total energy output per - unit time of a star. It is an intrinsic property of the star, not related to how bright it appears from Earth (which is apparent magnitude), its temperature average over life - cycle, or spectral shift.

Answer:

The amount of energy a star emits in a unit of time