When astronomers observe light from distant galaxies, they notice that the light appears redder than expected. This observation is known as redshift. Explain what redshift tells us about the motion of distant galaxies and what this suggests about the origin of the universe.

Eduqas GCSE Physics — 2.1 Light, lenses and the universe · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Redshift is the shift of light to longer wavelengths, i.e. towards the red end of the spectrum.
It shows that distant galaxies are moving away from us.
The further a galaxy is, the greater its redshift, meaning it is receding faster.
This supports the idea that the universe started from a single, very hot, dense point – the Big Bang.

Examiner tips

  • Use the term ‘redshift’ and explain it as a shift to longer wavelengths. Show the link between redshift and recession velocity. Mention the distance–redshift relationship. Conclude with the Big Bang origin.

Common mistakes

  • Confusing redshift with blueshift. Saying galaxies are moving towards us. Omitting the Big Bang explanation.

Mark scheme (4 marks)

  1. Redshift means the wavelength of light from distant galaxies is longer / shifted towards the red end of the spectrum
  2. Redshift indicates that distant galaxies are moving away from us
  3. The further away the galaxy, the greater the redshift / faster it is moving away
  4. This suggests the universe began from a single point in a very hot, dense state / the Big Bang

Key terms in this question

redshift · galaxies · universe

Related

More Light, lenses and the universe questions

▶ Try answering this question with AI marking (free) →