# Explain how the colour of a star can be used to determine its surface temperature, and describe how surface temperature relates to the position of a star on the Hertzsprung-Russell diagram.

> AQA A-Level Physics (7408) — 3.9.2 Classification of Stars · Explain · 5 marks

> Stars vary greatly in colour, from red to blue-white. The Hertzsprung-Russell (H-R) diagram plots stars according to their luminosity and surface temperature.

## Mark scheme (5 marks)

1. Hotter stars emit light that appears blue (or blue-white) / cooler stars appear red (or orange)
2. The colour/peak wavelength of light emitted shifts with temperature — hotter stars emit at shorter wavelengths
3. On the H-R diagram, surface temperature increases from right to left along the horizontal axis
4. Most stars lie along the main sequence — a diagonal band from top-left (hot, high luminosity) to bottom-right (cool, low luminosity)
5. Red giants / supergiants are found in the top-right (high luminosity, low temperature) and white dwarfs are found in the bottom-left (low luminosity, high temperature)

## Key terms

- [Hertzsprung-Russell diagram](https://www.gradenine.co.uk/glossary/hertzsprung-russell-diagram)
- [surface temperature](https://www.gradenine.co.uk/glossary/surface-temperature)

## 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-how-the-colour-of-a-c7d0367c) · Published by Druglandscape Ltd.