Question

if star a is intrinsically radiating less light than star b, which statement must be true? none of these statements must be true. star a is farther from earth than star b. star a appears fainter than star b. star a has a lower luminosity than star b. if star c appears equally as bright as star d as observed from earth, which statement must be true? none of these statements must be true. star c has the same luminosity as star d. star c is the same distance from earth as star d. star c and star d must have the same luminosity and distance.

Explanation:

1. Luminosity is the intrinsic amount of light a star radiates. If Star A is intrinsically radiating less light than Star B, by definition, Star A has a lower luminosity than Star B. Apparent brightness also depends on distance, so we can't say it appears fainter without knowing distances. And distance isn't determined just by intrinsic radiation.
2. Apparent brightness depends on both luminosity and distance. Just because two stars appear equally bright doesn't mean they have the same luminosity or are at the same distance. It could be that a more - luminous star is farther away and a less - luminous star is closer, resulting in the same apparent brightness.

Answer:

1. Star A has a lower luminosity than Star B.
2. None of these statements must be true.