Why do astronomers say that we are seeing the big bang with observations of the cosmic microwave background? Explain how such observations are powerful evidence in support of the big bang theory

the cosmic microwave background gives a snapshot of the universe when the temperature dropped enough to allow electrons and protons to form hydrogen atoms and by that making the universe nearly transparent to radiation as light was no longer scattered off free electrons.

Explanation:

the cosmic microwave background is the electromagnetic radiation filling all the space from the early stages of the universe and is the oldest dating to the epoch of recombination.