Question

How do scientists know that the universe is expanding? Question 2 options: a) The Doppler effect shows stars with red shifted light. b) The Doppler effect shows stars with blue shifted light. c)The Doppler effect shows stars with green shifted light. d)The Doppler effect shows stars with yellow shifted light.

Answer 1

The answer is A, which is often known as the red shift. It is the displacement of spectral lines toward longer wavelengths.