Might be worth mentioning the use of Doppler shift of the known patterns of spectral lines associated with elements to get information about radial velocity of

Might be worth mentioning the use of Doppler shift of the known patterns of spectral lines associated with elements to get information about radial velocity of e.g. a star being observed. https://www.e-education.psu.edu/astro801/content/l4_p7.html https://www.e-education.psu.edu/astro801/content/l4_p7.html Hyperfine splitting of spectral lines in hydrogen gas caused by the interaction between electron and neutron spin allows you to map the hydrogen in our local Galaxy. http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html As parent post says this is pretty standard astrophysics, just find any reasonable text in your local library. Or just Google 'astronomy .pdf' for a huge range of handbooks and presentations.