Lagrange point

A Lagrange point is a position in a rotating two-body system where gravity and centrifugal force balance in the rotating frame. A small object placed there can remain fixed relative to the two larger bodies.

Restricted three-body problem: A model of two massive bodies and a third body whose mass is too small to affect their motion. Lagrange points arise as equilibrium solutions of this model.
James Webb Space Telescope: A space telescope operating near the Sun–Earth L2 point to observe infrared light. Its orbit near L2 provides a stable observing geometry and a shielded, cold environment.
Joseph-Louis Lagrange: An Italian-born mathematician and astronomer whose work shaped analytical mechanics and celestial mechanics. He derived the triangular equilibrium solutions now associated with Lagrange points.
Keplerian orbit: An idealized orbit governed by the gravitational attraction of a single central mass. A Lagrange point is an equilibrium in a rotating system, not a Keplerian orbit.
Rotating reference frame: A coordinate system that rotates relative to an inertial frame, introducing apparent forces into equations of motion. Centrifugal force appears in the frame used to define Lagrange-point equilibrium.
Solar and Heliospheric Observatory: A joint NASA–ESA spacecraft that continuously observes the Sun from near the Sun–Earth L1 point. Its location near L1 gives it an uninterrupted view of the Sun.
Leonhard Euler: A Swiss mathematician whose work transformed analysis, mechanics, and astronomy. He identified the three collinear equilibrium configurations in the restricted three-body problem.
Libration point: A point in a rotating system where apparent forces balance; commonly used as another name for a Lagrange point. The alternate name emphasizes small oscillations around some equilibria.
L1: The collinear Lagrange point between two orbiting bodies. Its location between the bodies enables continuous views of the nearer body, as in solar observatories.
Geostationary orbit: A circular equatorial orbit in which a satellite matches Earth's rotation and appears fixed over one longitude. Unlike a Lagrange point, it is an orbit around one body rather than a force-balance location.

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