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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 thyis 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.
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