How has the Doppler effect and the redshift of stars and galaxies indicated that the universe is expanding?

1 Answer

In 1920, Edwin Hubble studies the spectrum of different galaxies and found that they have red shift in their spectra.

Explanation:

This indicates that the galaxies are moving away from us. He also found that the more the distance to galaxies, their recession speed is also high.

![http://astro.wku.edu](https://useruploads.socratic.org/vs0lZrePQH2LoT7KR4uH_images%20%281%29.jpg)

Red shift indicates that the galaxies are going away from us.
This is similar to Doppler shift in sound of a moving train.