In a spectroscopic analysis of a newly discovered high-redshift quasar, the characteristic Lyman-alpha hydrogen emission line is observed to have shifted from its rest-frame wavelength of 121.6 nm121.6\text{ nm}121.6 nm to a much longer wavelength in the infrared region.
Explain why the wavelength of this emission line has increased and state what this observation reveals about the motion of the quasar relative to Earth.
53 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift. Each one has a worked solution and a mark scheme showing where the marks go.