The simplest description of the form of the rotating nearly elliptical electronic orbit in the hydrogen atom is obtained by considering the chord which passes through the focus and is perpendicular to the major axis, the so-called "parameter." The length
of this parameter is given to a very close approximation by an expression of exactly the same form as the expression for the major axis, except that
takes the place of
. Using the same notation as before we have therefore
For each of the stationary states which had previously been denoted by a given value of