Which of the following is a measure of the amount of light a star directly emits? A. Luminosity B. Wavelength C. Brightness D. Intensity

Answer: A. Luminosity

Luminosity is defined as the amount of energy per unit of time emitted in all directions by a celestial body (a star).

Taking into account that all stars radiate light in a wide range of frequencies (or wavelengths) of the electromagnetic spectrum, this value is directly related to the absolute magnitude of the star and depends on its temperature and its area.