A star that is 100 pc distant from Earth has an apparent magnitude of m = +2.5. What is its absolute magnitude?
A) -7.5
B) +7.5
C) -2.5
D) -47.5

Question

Quizplus · Accepted Answer

The absolute magnitude of a star is defined as the magnitude it would have if it were placed at a distance of 10 parsecs from Earth. The formula to calculate absolute magnitude (M) from apparent magnitude (m) and distance in parsecs (d) is $M = m - 5 \log_{10}(d/10)$. Plugging in the given values, $M = 2.5 - 5 \log_{10}(100/10) = 2.5 - 5 = -2.5$.

A Star That Is 100 Pc Distant from Earth Has