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Emission Spectra (CIE A Level Physics)

Revision Note

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Emission spectra

  • Astronomers are very limited in how they can investigate objects in space
  • All of the techniques used involve analysing the light emitted from the star, or galaxy
  • One of these techniques involves analysing the emission and absorption spectra of stars
    • More details on this can be found in the revision note on Line Spectra
  • Elements in the star, predominantly hydrogen and helium, absorb some of the emitted wavelengths
  • Therefore, characteristic lines are present when the spectrum is analysed

Redshift on an emission spectrum

Stellar Emission Spectra, downloadable AS & A Level Physics revision notes

The top emission spectrum shows spectral lines of hydrogen measured on Earth. The bottom emission spectrum show the shifted spectral lines of hydrogen measured from a distant galaxy

  • When astronomers observe light from distant galaxies, they observe differences in the spectral lines to the light from the Sun
  • The lines have the same characteristic pattern, meaning the element can still be easily identified, they just appear to be shifted slightly
    • The lines in the spectra from distant galaxies show an increase in wavelength
    • The lines are moved, or shifted, towards the red end of the spectrum

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.