Rydberg constant
where formula_22 is the speed of light in vacuum, formula_23 is an experimentally determined constant (the Rydberg constant) and formula_24. Once the electron reached the lowest energy level (formula_25), it could not get any closer to the nucleus (lower energy). This approach also allowed Bohr to account for the Rydberg formula, an empirical description of the atomic spectrum of hydrogen, and to account for the value of the Rydberg constant formula_23 in terms of other fundamental constants.