Orbital precession

Orbital precession is the gradual change in an orbit’s orientation, caused by perturbations or relativistic effects. The orbit’s line of apsides can rotate within its plane, while its plane can tilt in space.

Apsidal precession: The rotation of an orbit’s line of apsides, which joins its nearest and farthest points from the central body. It is the in-plane form of orbital precession.
Mercury's perihelion precession: The observed advance of Mercury’s perihelion, produced by planetary perturbations and a relativistic correction. It is the classic measured case of apsidal precession.
Satellite orbit determination: The estimation of a satellite’s orbit from tracking measurements and a model of the forces acting on it. Accurate predictions must include secular rotations of orbital elements.
Orbital inclination: The angle between an orbital plane and a chosen reference plane. Inclination describes plane orientation at an instant; nodal precession describes its change.
Orbital elements: Parameters that specify an orbit’s size, shape, orientation, and position along its path. Precession is expressed as the time evolution of orientation-related elements.
Nodal precession: The rotation of an orbit’s ascending node, marking a change in the orientation of its orbital plane. It describes orbital precession through rotation of the plane in space.
Lunar apsidal precession: The rotation of the Moon’s line of apsides, completing a cycle in about 8.85 years. Solar perturbations make the Moon’s orbit precess much faster than a simple two-body model predicts.
Gravity field recovery: The inference of a body's gravitational field from measurements of spacecraft or satellite motion. Nodal and apsidal rates encode departures from a spherical gravity field.
Apsidal line: The line joining the nearest and farthest points of an orbit from its central body. Its orientation is the quantity that apsidal precession rotates.
Periapsis: The point in an orbit closest to the body being orbited. The changing direction toward periapsis defines apsidal rotation.

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