Astronomy clicker question: reionization

Astronomy 210, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle:

__________ is/are evidence of reionization in the early universe.

(A) Galaxy redshifts are proportional to galaxy distances.
(B) The near zero curvature of space-time.
(C) The amounts of helium and lithium in extremely old stars.
(D) Extremely distant galaxies surrounded by neutral hydrogen gas.
(E) The cosmic microwave background.
(F) (None of the above choices.)
(G) (I'm lost, and don't know how to answer this.)

Section 70160
(A) : 4 students
(B) : 1 student
(C) : 3 students
(D) : 10 students
(E) : 8 students
(F) : 0 students
(G) : 0 students

Correct = 38%

Correct answer: (D)

Reionization occurred when the first generation of stars formed the first galaxies, at the end of the dark ages. The light from these stars ionized hydrogen around them, creating emission nebulae.