Astronomers use the Doppler effect to:

  1. find how fast stars and galaxies move towards or away from us
  2. count stars
  3. find the colour of stars
  4. measure the mass of planets directly
Answer

A) find how fast stars and galaxies move towards or away from us

Red shift and blue shift. SLO P-11-D-04 · Understanding

Physics MCQ · More Wave Intensity and the Doppler Effect MCQs · Practise