Astronomers today use the concept proposed by christian doppler and edwin hubble to determine the motion of stars and galaxies. write a brief essay describing how the doppler effect explains why some stars are “blue shifted” and others are “red shifted.”

I am not going to write the answer for you, but I will point you in the right direction. Imagine yourself at a railroad track. If the sound of the train is getting fainter then it means the train is moving further away (red shift). If the sound of the train is getting louder, then the train is coming closer (blue shift). Instead of sound, we have frequency of light wave. The higher the frequency, the louder the train. The lower the frequency, the softer the train. Replace trains with stars. Also if you need more of a reference then reread the section on spectroscopy. I really hope this helps, I’m sorry I don’t want to just feed you an answer.

Best,
Mitanshu