Question

Quasar spectra often show many absorption lines that all appear to be as a result of the same electron transition (such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectrum. Why do we think this is the case?

Answer 1

Answer: Because of different redshift of cloud.

Step-by-step explanation:

We are seeing absorption lines from clouds of gas that lie between us and the quasar, and therefore each cloud has a different redshift.

A quasar's spectrum is hugely redshifted. And most astronomers think this large redshift tells us about the distance to the quasar.