Measuring Distance and Brightness: Practice Problem Solutions

1. Close one eye then the other: the finger seems to shift against the background. A nearby star shifts against far-away stars as Earth moves to opposite sides of its orbit.

2. d = 1 / 0.1 = 10 parsecs = 32.6 light-years.

3. d = 1 / 0.77 = about 1.3 parsecs (4.24 light-years).

4. 5 magnitudes means a factor of 100, so 100 times brighter.

5. It becomes 1/9 as bright (inverse-square law).

6. Apparent magnitude is how bright a star looks from Earth. Absolute magnitude is how bright it would look from 10 parsecs, a measure of its true brightness.

7. Magnitude −3 is brighter, by 5 magnitudes, which is a factor of 100.