Libration Points

(1) Points at which a body of small mass can be in a state of relative equilibrium with respect to two other celestial bodies (the restricted three-body problem). For a system of two bodies (considered as attracting mass points), there exist three collinear libration points lying on a straight line passing through these bodies and two triangular libration points located such that the two bodies and the libration points form equilateral triangles. In the case of collinear libration points, the bodies are in unstable equilibrium. The libration points of the earth-moon and the sun-earth systems are of particular importance in astrodynamics.

(2) The positions of relative equilibrium in the problem of celestial mechanics of the motion of a body of small mass in a force field that is independent of time in a rotating coordinate system.