20151215

Astronomy quiz question: current status of type Ia supernova seen tonight

Astronomy 210 Quiz 7, fall semester 2015
Cuesta College, San Luis Obispo, CA

A type Ia supernova in a distant galaxy seen in Earth's night sky tonight is currently a:
(A) protostar.
(B) white dwarf.
(C) planetary nebula.
(D) (None of the above choices.)

Correct answer (highlight to unhide): (D)

The finite speed of light means that it takes time for light from distant objects to reach the Earth. Thus looking at an object a given number of light years away means that it appears as it did that same number of years in the past. Since a type Ia supernova is the entire destruction of a white dwarf after rapidly stealing hydrogen from its companion star, then by the time observers on Earth see this explosion tonight, the white dwarf had already exploded in the past, and subsequently (and currently) nothing is left at that location.

Section 70158
Exam code: quiz07srrH
(A) : 8 students
(B) : 10 students
(C) : 11 students
(D) : 10 students

Success level: 29% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.62

Section 70160
Exam code: quiz07nM0r
(A) : 5 students
(B) : 8 students
(C) : 4 students
(D) : 8 students

Success level: 36% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.57

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