The shift of the hydrogen absorption spectrum of a galaxy provides evidence for the following:
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Motion of the galaxy - The Doppler effect causes a shift in the spectral lines of hydrogen due to the motion towards or away from us (redshift or blueshift).
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Expansion of the universe - The overall redshift observed in light from distant galaxies indicates that the universe is expanding, a key observation that supports the Big Bang theory.
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Composition of the universe - The specific absorption lines can be analyzed to determine the presence of hydrogen and other elements, giving insight into the composition of the universe.
Therefore, the three correct answers are:
- Motion of the galaxy
- Expansion of the universe
- Composition of the universe