Two questions about Lagrange points. (1) According to Wikipedia, "libration is a perceived oscillating motion of orbiting bodies relative to each other," whereas the Lagrange points are, with respect to two bodies, null points for a (real or hypothetical) third body with respect to the sum of the gravitational (or centrifugal: see next question) forces on that third body (assuming the third body's mass is negligible compared to each of the other two) . What do the two concepts have to do with one another so that they are considered identical? That is, (a) if something is at a Lagrange point, it is not oscillating, and (b) libration concerns the perception from an observer being on one of the two bodies bodies, whereas the Lagrange points concerns the state of an observer at a third point. I don't see the connection. (2) Some sites say the sum of the centrifugal forces, which is to say that there is no total inertia: the third body is motionless with respect to the two other bodies. In the situation in question, can you have one without the other: that is, where either (a) the sum of the gravitational forces is zero, but the sum of the centrifugal forces is not, or (b) the sum of the centrifugal forces is zero yet the sum of the gravitational forces is not? If either one of these is the case, then which one (gravitational or centrifugal) would be correct in the definition of Lagrange (or libration) points?