The Bohr radius constant is approximately equal to the most probable distance between the proton and electron in a hydrogen atom in its ground state. `a_0` is expressed in units of meters.
This constant is specified with a standard uncertainty (standard deviation) of: 0.00000000017 E-10 m
`a_0` = `(4pi*epsilon_0*h^2)/(m_e*e^2)`
The Bohr Radius is named after Niels Bohr, due to its role in the Bohr model of an atom.