Laplace Invariant Plane

a plane that passes through the center of mass of the solar system perpendicular to the angular momentum vector. The concept of the invariant plane was introduced in 1789 by P. Laplace, who pointed out the advantages in using it as a base coordinate plane in the study of the motions of the bodies of the solar system. Whereas the positions of the plane of the ecliptic and the equatorial plane continually vary, the Laplace invariant plane retains a fixed position in space. It is necessary to know the numerical values of the masses of all the planets in order to determine the position of the Laplace invariant plane relative to the plane of the ecliptic. Since these values are being continually refined with the development of astronomical studies, the parameters defining the position of the Laplace invariant plane are also changing somewhat. The position of the Laplace invariant plane with respect to the plane of the ecliptic at 1950.0 epoch is given by the following elements: the celestial longitude of the point of intersection with the ecliptic Ω = 107°13.3′±2.1′ and the inclination i = 1°38′49″±22″.