Who discovered the period-luminosity relationship, and why was it so critical?
What will be an ideal response?
Question 2
What happens to light passing through even thin clouds of dust?
A) The light that passes through them is blueshifted due to the cloud's approach.
B) Its motion causes all light to be redshifted as it passes through these clouds.
C) Its motion causes the light of stars beyond to twinkle.
D) Even a little can completely block all light, such as the Horsehead Nebula.
E) It dims and reddens the light of all more distant stars.
