Fine structure describes the splitting of the spectral lines of atoms due to electron spin and relativistic corrections to the non-relativistic Schrödinger equation. Hyperfine structure, with energy shifts typically orders of magnitudes smaller than those of a fine-structure shift, results from the interactions of the nucleus (or nuclei, in molecules) with internally generated electric and magnetic fields. Fine Structure Spin–orbit coupling is an interaction of a particle's spin with its motion. This interaction leading to shifts in an electron's atomic energy levels, due to electromagnetic interaction between the electron's spin and the magnetic field generated by the electron's orbit around the nucleus. This is detectable as a splitting of spectral lines, which can be thought of as a Zeeman effect due to the internal field. Hyperfine Structure The hyperfine structure is caused by interaction between magnetic field (from electron movement) and nuclear spin. Template:HideTOC Thumbnail: Schematic illustration of fine and hyperfine structure in hydrogen atom. (Public Domain; Edudobay ).