# Explain how scientists use the observed redshift of light from distant galaxies as evidence that the universe is expanding.

> Eduqas A-Level Physics — 4.3 Orbits and the wider universe · Explain · 5 marks

> When astronomers study the light from distant galaxies, they observe that the spectral lines in that light are shifted towards the red end of the spectrum compared to the same lines measured in a laboratory on Earth.

## Mark scheme (5 marks)

1. Redshift means the wavelength of light received from a galaxy is longer (shifted towards the red end) than expected
2. Redshift indicates that the galaxy is moving away from Earth / the source is receding
3. More distant galaxies show greater redshift, meaning they are moving away faster
4. Galaxies moving away in all directions suggests space itself is expanding
5. This supports the idea that the universe began from a single point / links to the Big Bang

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-scientists-use-the-observed-a2d3433f) · Published by Druglandscape Ltd.