# The universe contains billions of galaxies, each made up of billions of stars. Astronomers use the red-shift of light from distant galaxies to learn about the universe. Explain what red-shift tells astronomers about the movement of distant galaxies and about the origin of the universe.

> WJEC GCSE Physics (Wales) — 2.1 Light, lenses and the universe · Explain · 4 marks

> Light from distant galaxies shows that the wavelengths of known spectral lines are shifted towards the red end of the spectrum. The further away a galaxy is, the greater the shift observed.

## Mark scheme (4 marks)

1. Red-shift means the wavelength of light from distant galaxies is increased (shifted towards longer wavelengths / towards the red end of the spectrum)
2. Red-shift shows that distant galaxies are moving away from us / the Earth
3. The greater the red-shift, the faster / the further away the galaxy is moving away
4. This evidence supports the Big Bang theory — the universe began from a single point and has been expanding ever since

## Key terms

- [red-shift](https://www.gradenine.co.uk/glossary/red-shift)
- [universe](https://www.gradenine.co.uk/glossary/universe)

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/the-universe-contains-billions-of-galaxies-3d7eee16) · Published by Druglandscape Ltd.