 That is,
is an approximation of

Theoretical models may calculate the constants (coefficients) corresponding to the higher powers of "T", but since it is impossible for a (finite) polynomial to match a periodic function over all numbers, the difference in all such approximations will grow without bound as "T" increases.However, greater accuracy can be obtained over a limited time span by fitting a high enough order polynomial to observation data, rather than a necessarily imperfect dynamic numerical model.So for present flight trajectory calculations of artificial satellites and spacecraft, the polynomial method gives better accuracy.