The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4. From this information (assuming that the starlight has not been dimmed by interstellar clouds), one can say for sure that Alderamin is _____.
A) less than 10 pc away
B) brightest in blue light
C) brightest in red light
D) more than 10 pc away

Question

Quizplus · Accepted Answer

The apparent magnitude of a star becomes fainter (increases) as the distance from the observer increases. Since Alderamin's absolute magnitude (1.4) is brighter than its apparent magnitude (2.4), it indicates that the star is located at a distance where its light is dimmed due to the distance, which happens when a star is more than 10 parsecs away. Absolute magnitude is defined as the apparent magnitude a star would have if it were 10 parsecs away. If a star's apparent magnitude is fainter than its absolute magnitude, it must be farther than 10 parsecs.

The Star Alderamin Has an Apparent Magnitude of 2