secular perturbation

Secular perturbation in astronomy refers to a gradual, long-term change in the orbital path of a celestial object. This deviation from a simple elliptical orbit is caused by the gravitational influence of other celestial bodies. For instance, the Moon's orbit is perturbed by the Sun, causing its orbital nodes to regress over time. Similarly, the orbits of artificial satellites are affected by Earth's non-spherical shape, particularly its equatorial bulge. These perturbations cause orbital elements, which would otherwise be constant, to vary slowly over extended periods. The study of these perturbations has been crucial in astronomical discoveries, such as the prediction and discovery of Neptune due to irregularities in Uranus's orbit.123