Final answer:
The widespread acceptance of the Big Bang model is primarily due to the discovery of the cosmic microwave background radiation and the observation of the expansion of the universe, both of which are predicted by the Big Bang theory.option b is correct.
Step-by-step explanation:
Key Observational Facts Supporting the Big Bang Theory
The two key observational facts that led to widespread acceptance of the Big Bang model are the cosmic microwave background (CMB) radiation and the expansion of the universe. The discovery of the CMB, which acts as a blackbody radiation with a temperature of about 2.73 K, provided evidence of the early, hot, and dense state of the universe. This background radiation was predicted by the Big Bang model and its uniformity across the sky suggested a common origin for all regions of the universe. Additionally, the observable expansion of the universe, indicated by the redshift of light from distant galaxies, directly points to a universe that was once much smaller and has been growing over time, consistent with the Big Bang theory.
The CMB was detected as the afterglow from the time when the universe became transparent to radiation, about 380,000 years after the Big Bang, and the photons from that era have been freely streaming through space ever since. The expansion of the universe is inferred from the observation that galaxies are moving away from us, with more distant galaxies receding at greater velocities—a phenomenon captured in Hubble's law, which describes this relationship between distance and recession speed.