| Astrophysics (index) | about |
Hyperfine structure of atomic energy levels and spectral lines are energy-level-transitions due to spin and magnetic interactions between electrons and the nucleus (hyperfine levels). They are orders-of-magnitude smaller than fine structure transitions, which, in turn is orders of magnitude smaller than gross structure transitions from electron movement between larger/smaller electron shells (all the potential electron orbits that have a certain orbital radius), that form lines such as hydrogen's Balmer series.
A hyperfine structure line widely used in astrophysics is hydrogen's 21cm line, due to its one electron changing its spin.