It is the position in space where combined gravitational force of two large bodies such as Earth and Sun, equal the centrifugal force felt by much smaller 3rd body. It is a point of equilibrium where a spacecraft may be "parked" to make observations. There are 5 such points between Earth and Sun. - Lagrange points are points of gravitational equilibrium for a third body in a two-body system. - They are used for positioning spacecraft for stable observations. - There are five Lagrange points (L1 to L5) for any two orbiting bodies.