The average red giant is about 1,000 times more luminous than the average main-sequence star.If both kinds of stars have about the same brightness in our night sky, how much farther away are the red giants compared to the main-sequence stars?
A) 32 times farther
B) 1,000 times farther
C) 65 times farther
D) 5.6 times farther
E) The red giants and main-sequence stars are approximately the same distance away.

Question

Quizplus · Accepted Answer

The luminosity-distance relationship states that if two stars have the same apparent brightness, the one that is more luminous must be farther away. The distance is proportional to the square root of the luminosity ratio. Since red giants are 1,000 times more luminous, they are √1000 ≈ 32 times farther away.

The Average Red Giant Is About 1,000 Times More Luminous