Final answer:
To measure a star's true brightness, or luminosity, you need to know its distance, apparent brightness, and color or temperature, which is answer option b.
Step-by-step explanation:
To measure a star's true brightness, or luminosity, one needs to know its distance, apparent brightness, and color or temperature. Therefore, the correct answer to the question is option b. Its distance, apparent brightness, and color or temperature. The apparent brightness of a star depends on both its luminosity and its distance from Earth. These factors are crucial because a star may appear dim if it is of low luminosity and nearby, or if it is of high luminosity but far away. Techniques such as the period-luminosity relation for Cepheid variable stars allow astronomers to determine a star's luminosity. Once the luminosity is known, astronomers can compare it with the star's apparent brightness to calculate the distance to the star.