# Astronomers studying a distant star detect that certain wavelengths of visible light are missing from the continuous spectrum of radiation received from the star. Explain why specific wavelengths are absent and describe what information astronomers can obtain from the pattern of missing wavelengths.

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

> When light from a distant star is spread into a spectrum, dark lines are observed at specific positions across the continuous background of colours.

## Mark scheme (5 marks)

1. The continuous spectrum of light is produced by the hot, dense core/surface of the star
2. As light passes through the cooler outer atmosphere/gas of the star, certain wavelengths are absorbed
3. Each element absorbs a unique/characteristic set of wavelengths, producing a unique pattern of dark lines
4. By comparing the pattern of dark lines to known laboratory spectra, astronomers can identify which elements are present in the star's atmosphere
5. If the dark lines are shifted towards the red end of the spectrum (red-shifted), the star is moving away from Earth / the shift in position of the lines can indicate the star's speed or direction of movement

## Key terms

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

## 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/astronomers-studying-a-distant-star-detect-ffac7e08) · Published by Druglandscape Ltd.