Observing M87’s spectral of light

The galaxy M87, shown in Figure 15.5, was discovered by Charles Messier in 1781. Located
54 million light-years from Earth, it is one of the most massive galaxies in the Universe,
including a black hole at its centre that is 4 billion times more massive than the Sun. Observing
the spectrum of M87’s light, we detect the spectral pattern of hydrogen. Use this information
to determine the wavelength at which we observe the red spectral line of hydrogen. Show how
you got your answer.

(A) 650 nm
(B) 654 nm
(C) 656 nm
(D) 659 nm
(E) 662 nm

I got 656 nm. My reasoning for picking (C) is that I looked up the wavelength spectrum for Hydrogen in my textbook and for red spectral line in Hydrogen is approximately 656.3 nm, so I assume it is 656 nm for the final answer.

I don’t think it has anything to do with redshift and blueshift so I believe my answer is correct, but please correct me if I am missing something.


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