Lagrangian Point
  • Points in a two-body orbital system (like the Earth and the Moon, or the Sun and Jupiter), where matter can be placed stably without being pulled towards either object. The Earth-Moon system has five Lagrangian points, L 1, 2, 3, 4 and 5, at which dust appears to accumulate. Two of the points are ahead of and behind the Moon in the same orbit (L4, L5) and the other three are opposite the Moon in the same orbit (L3) and on the Earth-Moon line just this side of (L1) and beyond (L2) the Moon. Other cases of matter accumulating at Lagrangian points are also known in the solar system, notably the Trojan asteroids in Jupiter’s orbit, 60¦ ahead of or behind it. Another case is 1980 S6, a tiny satellite of Saturn in the same orbit as Saturn’s satellite Dione and 60¦ ahead of it. Joseph Louis Lagrange (1736–1813) originally developed the idea of Lagrangian points in the context of the Jupiter/Sun system.

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