Astronomers observing the absorption spectra of distant galaxies notice that key spectral lines are shifted towards the longer wavelength (red) end of the spectrum compared to a laboratory reference source. Explain how the relationship between the size of this red-shift and the distance of galaxies from Earth provides evidence that the Universe is expanding.
53 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.