A spectrometer on a space telescope measures the emission spectrum of a distant quasar and detects a systematic shift in its spectral lines towards the infra-red.
Explain what is meant by this red-shift and state the physical reason for this shift.
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.