"Arnold Sommerfeld

? introduced the

**fine-structure constant** in 1916, as part of his theory of the relativistic deviations of atomic spectral lines from the predictions of the Bohr model

?. The first physical interpretation of the

**fine-structure constant α** was as the

ratio of the

velocity of the

electron in the first circular orbit of the relativistic Bohr atom to the

speed of light in the

vacuum. Equivalently, it was the quotient between the maximum

angular momentum allowed by relativity for a closed orbit, and the minimum

angular momentum allowed for it by

quantum mechanics. It appears naturally in Sommerfeld's analysis, and determines the size of the splitting or fine-structure of the hydrogenic spectral lines."

Wikipedia, fine structure constant
See Also

**Fine Structure**
**Hyperfine Structure**
**Spectra**