# A distant galaxy is observed to emit electromagnetic radiation. The peak wavelength of this radiation is shifted towards longer wavelengths compared to the same radiation measured from a laboratory source on Earth. Explain what this observation tells astronomers about the galaxy and what it suggests about the universe as a whole.

> WJEC A-Level Physics (Wales) — 1.6 Using radiation to investigate stars · Explain · 5 marks

## Mark scheme (5 marks)

1. The shift towards longer wavelengths is called red-shift
2. Red-shift indicates the galaxy is moving away from Earth / the observer
3. The greater the red-shift, the greater the speed at which the galaxy is moving away / the further away the galaxy is, the faster it recedes
4. Galaxies in all directions show red-shift, suggesting the universe is expanding
5. This expansion supports the idea that the universe began from a single point / supports the Big Bang theory

## Key terms

- [electromagnetic radiation](https://www.gradenine.co.uk/glossary/electromagnetic-radiation)
- [peak wavelength](https://www.gradenine.co.uk/glossary/peak-wavelength)
- [universe](https://www.gradenine.co.uk/glossary/universe)

## Related

- [Revision notes for WJEC A-Level 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/a-distant-galaxy-is-observed-to-9273e1ca) · Published by Druglandscape Ltd.