Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q8.2
Refer to the table below in answering the following question.
| m apparent magnitude | M absolute magnitude | |
| Sirius | –1.47 | +1.4 |
| Canopus | –0.72 | -3.1 |
| Capella | +0.05 | -0.7 |
| Rigel | +0.14 | -6.8 |
| Fomalhaut | +1.15 | +1.9 |
[Version 1]
[3.0 points.] Which one of the following choices best corresponds to the star that is the farthest from the Earth?
(A) Sirius.
(B) Canopus.
(C) Capella.
(D) Rigel.
(E) Fomalhaut.
Correct answer: (D)
A star 10 parsecs away will have the same value for apparent and absolute magnitude. A star that is farther than 10 parsecs away will "brighten when brought closer" to the standard 10 parsec distance, and thus its absolute magnitude should be brighter than its apparent magnitude. What is notable for this version of this question is that many students selected Fomalhaut, which most nearly at the standard 10 parsec distance (actually slightly farther than 10 parsecs away).
Student responses
Section 0135
(A) : 2 students
(B) : 3 students
(C) : 1 student
(D) : 9 students
(E) : 14 students
[Version 2]
[3.0 points.] Which one of the following choices best corresponds to the star that is the nearest to the Earth?
(A) Sirius.
(B) Canopus.
(C) Capella.
(D) Rigel.
(E) Fomalhaut.
Correct answer: (A)
A star 10 parsecs away will have the same value for apparent and absolute magnitude. A star that is closer than 10 parsecs away will "dim when pushed away" to the standard 10 parsec distance, and thus its absolute magnitude should be dimmer than its apparent magnitude.
Student responses
Section 1073
(A) : 23 students
(B) : 3 students
(C) : 5 students
(D) : 7 students
(E) : 4 students
Section 1073, which was asked for the nearest star on their quiz, was given this same question, but asked for the farthest star on a subsequent midterm.
ReplyDeleteCorrect response: (D) (farthest)
Student responses
Section 1073
(A) : 6 students
(B) : 3 students
(C) : 1 student
(D) : 24 students
(E) : 8 students
Student 5450 wrote in the following comments to help answer this question (correctly), referring to the apparent magnitude of each star, and how it would turn into absolute magnitude once it is brought to the standard distance of 10 parsecs:
Sirius: "bright push back to +10" [crossed out]
Canopus: "bright pull forward to 10"
Capella: "dim pull forward to 10"
Rigel: "pull way forward to 10"
Fomalhaut [crossed out]