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In lunar astronomy, libration is the cyclic variation in the apparent position of the Moon perceived by Earth-bound observers and caused by changes between the orbital and rotational planes of the moon. It causes an observer to see slightly different hemispheres of the surface at different times.
The James Webb Space Telescope (JWST) is in a libration point orbit around the L2 Lagrange point of the Sun, and Earth-Moon barycenters. [ 2 ] [ 3 ] Because libration point orbits are quasiperiodic, the telescope must make frequent small burns to maintain proximity to the L2 point, as part of orbital station keeping , limiting the lifespan of ...
In 2011, NASA transferred two of its THEMIS spacecraft from Earth orbit to Lunar orbit by way of Earth–Moon L1 and L2 Lissajous orbits. [ 11 ] In June 2018, Queqiao , the relay satellite for China's Chang'e 4 lunar lander mission, entered orbit around Earth-Moon L2.
The lunar theory, as developed numerically to fine precision using these modern measures, is based on a larger range of considerations than the classical theories: It takes account not only of gravitational forces (with relativistic corrections) but also of many tidal and geophysical effects and a greatly extended theory of lunar libration ...
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Lunar_libration_with_phase.ogv (Ogg multiplexed audio/video file, Theora/Vorbis, length 5.9 s, 600 × 600 pixels, 486 kbps overall, file size: 349 KB) This is a file from the Wikimedia Commons . Information from its description page there is shown below.
It is accurate enough to use in a novelty clock application showing lunar phase, but specialist usage taking account of lunar apogee and perigee requires a more elaborate calculation. Also, due to lunar libration it is not uncommon to see up to 101% of the full moon or even up to 5% of the lunar backside.
Libration causes variability in the portion of the Moon visible from Earth. This is an artificial animation of one lunar orbit; in reality, the visible hemisphere would go through phases of dark and light as the Moon rotates with respect to the Sun.