Question

A measure of the amount of light given off by a star is its _____.

Answer 1

A measure of the amount of light given off by a star is its luminosity. 
It is the intrinsic brightness of a celestial object (as distinct from its apparent brightness diminished by distance).

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Answer 2

A measure of the amount of light given off by a star is its absolute luminosity or magnitude. Absolute magnitude is the measure of intrinsic brightness of a celestial object. It is the hypothetical apparent magnitude of an object at a standard distance of exactly 10 parsecs (32.6 light years) from the observer, assuming no astronomical extinction of starlight.