A path around the L₁ or L₂ Lagrangian points of a two-body system. Lissajous orbits are utilized by certain spacecraft that are required to be in a stable position relative to the Earth and Sun while making long-term observations. In a Lissajous orbit the spacecraft follows a natural (but complex) motion that requires the minimum amount of energy for station-keeping, unlike a halo orbit, in which the craft follows a simple circular or elliptical path. Spacecraft placed into a Lissajous orbit around the Sun–Earth L₂ point include the Herschel Space Observatory and Planck. The James Webb Space Telescope will also be placed in a Lissajous orbit at the same location. Such orbits are named after the French mathematician Jules Antoine Lissajous (1822–80), who studied the types of curves followed by an object in such a position.