# 14: General Perturbation Theory

- 14.4: Lagrange's Planetary Equations
- Lagrange’s Planetary Equations enable us to calculate the rates of change of the orbital elements if we know the form of the perturbing function.

*Thumbnail: Animation showing the relationship between the five Lagrangian points (red) of a planet (blue) orbiting a star (yellow), and the gravitational potential in the plane containing the orbit (grey surface with purple contours of equal potential). Image used with permission (CC BY-SA 4.0; cmglee).*