Redshifted Spectra of Selected Galaxies
The photos below show several selected galaxies each traveling outward in space with a different velocity of recession. The vertical yellow arrow points to a small segement of the galaxy's spectrum that is of interest to us; it is the bright hydrogen line displayed in the far right of the laboratory spectrum (shown just above and below the galaxy spectrum as a reference). Look carefully and you will also see a left pointing horizontal arrow which indicates the extent of the shift as compared to the laboratory based spectra which are shown above and below that of the galaxy spectrum. Study the diagrams carefully, and you will notice that the spectra for each galaxy is shifted, with those moving at a higher velocity displaying the greatest doppler redshift (in this case the velocity of the galaxy has been calculated for you. In the raw data form the horizontal axes of the spectra would be labelled "wavelength" or "energy." Measuring the shift in wavelength from the laboratory frame would enable you to calculate the galaxy's velocity.) The distances given for these galaxies have been obtained by other independent methods.
From J. Silk, The Big Bang