The Expanding Universe

In the 20s and 30s, Edwin Hubble noticed that emission lines in the spectra of spiral nebulae were consistently red shifted.
- The smaller the angular size of the nebula, the greater the red shift.
- Once he measured the distance to Andromeda, he was able to express a relationship between the measured velocity and the distance.
  - V=H0d
  - Added benefit, v is much easier to measure than d

In the 20s and 30s, Edwin Hubble noticed that emission lines in the spectra of spiral nebulae were consistently red shifted.