Which property of a star indicates its total output of energy?

Luminosity is the intrinsic property of a star that measures its total output of energy emitted per unit of time, typically expressed in watts. It reflects the actual energy production of the star, independent of its distance from the observer. This is crucial for understanding the physical processes occurring within the star, such as nuclear fusion and temperature, as luminosity is closely related to a star's size and temperature, according to the Stefan-Boltzmann law.

In contrast, brightness refers to how bright a star appears from Earth, which can vary due to distance and atmospheric conditions, making it a less reliable measure of a star's energy output. Magnitude is a system of classifying stars based on their brightness, rather than their luminosity. Color index provides information about a star's temperature based on the color of the light it emits, but it does not directly reflect total energy output. Therefore, luminosity stands out as the most relevant property for indicating a star's entire energy production.