Astronomers use spectrometers to study the light from stars. Explain how the absorption line spectrum of a star can be used to determine the chemical composition of the star's atmosphere, and why the lines appear at specific positions in the spectrum.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When light from a star passes through a spectrometer, a series of dark lines is observed against a continuous background of colours.
Model answer (5 marks)
The star emits a continuous spectrum from its hot interior/photosphere. In the overlying atmosphere atoms absorb photons of only certain energies, producing dark absorption lines at specific wavelengths.
1. The continuous spectrum is produced by the hot interior/surface (photosphere) of the star.
2. Atoms in the star's atmosphere absorb specific wavelengths/frequencies of light.
3. Each element absorbs only specific wavelengths unique to that element, producing dark lines at those positions.
4. The pattern/positions of the dark lines can be matched to known spectra of elements measured in a laboratory.
5. The elements whose absorption patterns match the observed dark lines are identified as being present in the star's atmosphere.
1. The continuous spectrum is produced by the hot interior/surface (photosphere) of the star.
2. Atoms in the star's atmosphere absorb specific wavelengths/frequencies of light.
3. Each element absorbs only specific wavelengths unique to that element, producing dark lines at those positions.
4. The pattern/positions of the dark lines can be matched to known spectra of elements measured in a laboratory.
5. The elements whose absorption patterns match the observed dark lines are identified as being present in the star's atmosphere.
Examiner tips
- Use the word "absorption" and mention the photosphere; match each point to the mark scheme; give a clear example of matching laboratory spectra; keep answer concise and in student voice.
Common mistakes
- Confusing emission lines with absorption lines; not mentioning the photosphere as source of continuous spectrum; failing to explain why lines are at specific positions (unique energy levels).
Mark scheme (5 marks)
- The continuous spectrum is produced by the hot interior/surface (photosphere) of the star
- Atoms in the star's atmosphere absorb specific wavelengths/frequencies of light
- Each element absorbs only specific wavelengths unique to that element, producing dark lines at those positions
- The pattern/positions of the dark lines can be matched/compared to known spectra of elements measured in a laboratory
- The elements whose absorption patterns match the observed dark lines are identified as being present in the star's atmosphere
Key terms in this question
absorption line spectrum · chemical composition
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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