definition 
Five locations in space where the centrifugal force and the gravitational force of
two bodies (m orbiting M) neutralize each other. A third, less massive body, located
at any one of these points, will be held in equilibrium with respect to the other
two. Three of the points, L1, L2, and L3, lie on a line joining the centers of M and
m. L1 lies between M and m, near to m, L2 lies beyond m, and L3 on the other side
of M beyond the orbit. The other two points, L4 and L5, which are the most stable,
lie on either side of this line, in the orbit of m around M, each of them making an
equilateral triangle with M and m. L4 lies in the m's orbit approximately 60° ahead
of it, while L5 lies in the m's orbit approximately 60° behind m.

