Galactic tide and secular orbital evolution

Equation of motion for the galactic tide is treated for the case of a comet situated in the Oort cloud of comets. We take into account that galactic potential and mass density depend on a distance from the galactic equator and on a distance from the rotational axis of the Galaxy. Secular evolution of orbital elements is presented. New terms generated by the Sun's oscillation about the galactic plane are considered. The inclusion of the new terms into the equation of motion of the comet leads to orbital evolution which may be significantly different from the conventional approach. The usage of the secular time derivatives is limited to the cases when orbital period of the comet is much less than i) the period of oscillations of the Sun around the galactic equator, and, ii) the orbital period of the motion of the Sun around the galactic center.