Astronomers observing the light spectra from distant galaxies notice that the prominent absorption lines are shifted towards the red end of the spectrum (red-shifted) compared to those observed in a laboratory on Earth.
Explain how this red-shift provides evidence that the Universe is expanding.
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.