# Explain why astronomers observe that light from distant galaxies appears shifted towards the red end of the electromagnetic spectrum, and describe what this observation tells us about the universe.

> Eduqas A-Level Physics — 6.3 Stellar evolution and cosmology (A-Level only) · Explain · 5 marks

> When astronomers study the light from distant galaxies, they find that the frequencies of known spectral lines are lower than expected.

## Mark scheme (5 marks)

1. The galaxies are moving away from us / the Earth / our galaxy
2. As a source moves away, the observed wavelength of its light increases / frequency decreases (redshift)
3. The more distant the galaxy, the greater the redshift / the faster it is moving away
4. This tells us the universe is expanding
5. This supports the idea that the universe began from a single point / the Big Bang

## Key terms

- [electromagnetic spectrum](https://www.gradenine.co.uk/glossary/electromagnetic-spectrum)

## Related

- [Revision notes for Eduqas A-Level Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-astronomers-observe-that-light-68799377) · Published by Druglandscape Ltd.