Regarding Hubble's observation of the red-shifting of galaxies' light: what standard was he measuring against the light being red-shifted? The Sun? If so, surely it could have been accounted for by the different types of stars and the different frequencies they emit?

Question

anonymous · Answer

The red shift of galaxies is determined by looking at their spectral lines. The lines produced by different elements occur at very specific places. If the lines are shifted from the location from objects that aren't moving, the amount they are shifted can be used to determine the velocity of the source.