Final answer:
The phenomena that stars are moving away from Earth, which indicates the universe is expanding, was first identified through the red shift in distant galaxies' hydrogen spectra by Edwin Hubble. This observation, known as Hubble's law, supports the Big Bang theory and reveals that the universe's expansion is accelerating.
Step-by-step explanation:
The Expanding Universe and Its Observation
The observation that stars are moving away from Earth is evidence that the universe is expanding. This idea was first put forth by Edwin Hubble, when he observed the red shift in the hydrogen spectra of distant galaxies. The further away a galaxy is, the more pronounced this shift, which implies that galaxies are receding faster when they are farther from us. This relationship between the red shift and distance is expressed in Hubble's law.
Hubble's discovery led to the proposal of the Big Bang theory, which posits that the universe began from a singular explosion, throwing matter into space. Over time, it became clear that the universe's expansion is not only ongoing but also accelerating. This accelerated expansion was not anticipated by astronomers and was substantiated through observations of distant supernovae and the red shifts associated with their light as it reaches Earth.
It is important to understand that this cosmological red shift is due to the expansion of space itself, not because galaxies are moving through space. The implication of this is profound—although we see objects moving away from us, there is no center of expansion in the universe; all points in space witness the same expansion relative to themselves.