# Explain why astronomers began building radio telescopes in addition to optical telescopes, and describe one advantage and one disadvantage of using a radio telescope compared to an optical telescope.

> AQA A-Level Physics (7408) — 3.9.1 Telescopes · Explain · 5 marks

## Mark scheme (5 marks)

1. Radio telescopes detect radio waves (from space) / different part of the electromagnetic spectrum to optical telescopes
2. Some astronomical objects / phenomena emit radio waves but little or no visible light, so optical telescopes cannot detect them
3. Advantage: radio waves pass through dust clouds / gas clouds / Earth's atmosphere without being absorbed / scattered, so observations are not blocked
4. Disadvantage: radio telescopes need to be very large (much larger than optical telescopes) to produce a detailed / high-resolution image
5. Disadvantage must be correctly identified as a limitation of radio telescopes (not a general disadvantage of any telescope) — mark is awarded only if the disadvantage stated is specific and scientifically valid

## Key terms

- [radio telescope](https://www.gradenine.co.uk/glossary/radio-telescope)
- [optical telescope](https://www.gradenine.co.uk/glossary/optical-telescope)

## Related

- [Revision notes for AQA A-Level Physics (7408)](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/explain-why-astronomers-began-building-radio-5a348400) · Published by Druglandscape Ltd.