Glossary / Space
Lagrange point
Five points where the gravity of two bodies, such as the Sun and Earth, balances the motion of orbiting around them, so a small object can hold its position.
The mutual motion of three bodies generally cannot be solved exactly, but in 1772 Joseph-Louis Lagrange found special solutions, including five points where a third body keeps a fixed arrangement relative to the other two[1].
L1, between the Sun and Earth, gives an uninterrupted view of the Sun; L2, beyond Earth, keeps the Sun, Earth and Moon in one direction, ideal for telescopes. ISEE-3 was the first spacecraft placed at L1, in 1978; the James Webb Space Telescope orbits near L2.
Related terms
- Kepler's lawsThree laws of planetary motion: planets move on ellipses with the Sun at one focus, sweep faster when closer to it, and have orbital periods tied to orbit size.
- Hohmann transferMoving between two circular orbits by riding an ellipse tangent to both, with just two burns — a fuel-efficient way to transfer.
On the timeline
Sources
- J.-L. Lagrange, “Essai sur le problème des trois corps,” Prix de l'Académie royale des sciences de Paris, tome IX (1772).