in astronomy, a point in the orbital plane of two massive objects circling about their centre of gravity where a smaller mass can remain in equilibrium
There are five Lagrangian points but only two, 60° either side of the less massive body and in the same orbit, can be stable. The two groups of Trojan asteroids, which share the orbit of Jupiter, are trapped at the two stable Lagrangian points in the Sun-Jupiter system — Dr Jacqueline Mitton
[named after Joseph Louis Lagrange d.1813, French mathematician and astronomer]