• Astronomers are very limited in how they can investigate objects in the 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 notes “Line Spectra” in the Quantisation of Energy topic
• Elements in the star, predominantly hydrogen and helium, absorb some of the emitted wavelengths
• Therefore, characteristic lines are present when the spectrum is analysed

The top emission spectra shows spectral lines of hydrogen measured on Earth

The bottom emission spectra shows 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 sightly
  • 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