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.

Notes

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)`

• `m_e` - electron mass
• e - elementary charge
• h - reduced Planck's constant
• 1/(`4pi*epsilon_0`) - Coulomb Force Constant

The Bohr Radius is named after Niels Bohr, due to its role in the Bohr model of an atom.