Bessel functions appear as coefficients in the series expansion of the indirect perturbation of a planet, that is the motion caused by the motion of the Sun caused by the perturbing body.
Bessel function lalabas bilang coefficients sa serye pagpapalawak ng tuwiran pagkaligalig ng isang planeta, na ang kilos ay sanhi ng paggalaw ng Sun na sanhi ng perturbing katawan.