Final answer:
The "brightest star" would correspond to magnitude -1, as the magnitude scale used in astronomy is an inverse one in which lower numbers indicate brighter stars. With negative magnitudes denoting the brightest objects, magnitude -1 represents the brightest option listed.
Step-by-step explanation:
The magnitude system used in astronomy ranks stars according to their apparent brightness as seen from Earth. A lower magnitude number corresponds to a brighter star, with negative magnitudes representing exceptionally bright objects. Therefore, among the options given (a. 1 b. -1 c. 3 d. 0), the "brightest star" would correspond to magnitude -1 since it is the lowest number and magnitude values are inversely related to brightness.
For example, Sirius, the brightest star in the night sky, has a magnitude of -1.5, making it brighter than a star with a magnitude of 0 or 1. The magnitude scale is logarithmic; each step in magnitude represents a fixed ratio in brightness. A difference of 5 magnitudes corresponds to a brightness difference of 100 times, with each magnitude step representing approximately 2.5 times change in brightness. Hence, a star with magnitude 1 is brighter than those with magnitudes of 3 or 16.