## 20101025

### Astronomy quiz question: apparent vs. absolute magnitude

Astronomy 210 Quiz 4, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

[Version 1]

Fomalhaut is a star that is located 7.7 parsecs away from Earth. If Fomalhaut were moved to a location 10 parsecs away, its apparent magnitude m would __________, while its absolute visual magnitude M_V would __________.
(A) get dimmer; not change.
(B) get brighter; not change.
(C) not change; get dimmer.
(D) not change; get brighter.

The apparent magnitude of Fomalhaut, which is the brightness as seen from Earth, will get dimmer as it is moved farther away from 7.7 parsecs to 10 parsecs. The absolute visual magnitude, which is the intrinsic brightness, will remain the same no matter where Fomalhaut is located.

Section 70158
(A) : 33 students
(B) : 0 students
(C) : 8 students
(D) : 2 students

"Success level": 75% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75

[Version 2]

Antares is a star that is located 190 parsecs away from Earth. If Antares were moved to a location 10 parsecs away, its apparent magnitude m would __________, while its absolute visual magnitude M_V would __________.
(A) get dimmer; not change.
(B) get brighter; not change.
(C) not change; get dimmer.
(D) not change; get brighter.

The apparent magnitude of Antares, which is the brightness as seen from Earth, will get brighter as it is moved closer from 190 parsecs to 10 parsecs. The absolute visual magnitude, which is the intrinsic brightness, will remain the same no matter where Antares is located.

Section 70160
(A) : 4 students
(B) : 28 students
(C) : 1 students
(D) : 8 students

"Success level": 70% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73