Light from stars provides evidence that the universe is expanding. Which two statements explain how light from the stars indicates the universe is expanding?
A. The light waves are closer together than predicted.
B. The light waves get "stretched out" as they travel.
C. The light waves appear redder than expected.
D. The light waves look bluer than they should.

B. The light waves get "stretched out" as they travel.

C. The light waves appear redder than expected.

Explanation:

You might hear about doppler effect before. An ambulance siren will be heard differently when it coming to you and when it moves away. When moving away, the frequency of the sound will seem to keep getting lower to the observer. A lower frequency means the sound appear to have a longer wavelength.

When scientist examines the lightwave from the distant stars, they find that the light wavelength seems stretched out and then it should be. The light also seems redder than expected. Redder light means the wavelength is longer, so the object should move away from our observation point.