libration
Sign in to savethumb|The lunar phases and librations in 2019 in the Northern Hemisphere at hourly intervals, with music, titles, and supplemental graphics alt=Over one lunar month more than half of the Moon's surface can be seen from the surface of the Earth.|thumbtime=0:02|thumb|Simulated views of the Moon over one month, demonstrating librations in latitude and [[longitude. Also visible are the different phases, and the variation in visual size caused by the variable distance from the Earth.]] thumb|Theoretical extent of visible lunar surface (in green) due to libration, compared to the extent of the visib
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Libration is a slight rocking or wobbling motion that allows us to see slightly more than half of the Moon's surface over time, even though the same side always faces Earth. This matters because it means that from Earth, we can eventually observe about 59% of the Moon's surface rather than just 50%, giving us a more complete view of our nearest celestial neighbor.
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Article
7 sectionsContents
- Lunar libration
- Physical libration
- Forced physical libration
- Free physical libration
- See also
- References
- External links
thumb|The lunar phases and librations in 2019 in the Northern Hemisphere at hourly intervals, with music, titles, and supplemental graphics alt=Over one lunar month more than half of the Moon's surface can be seen from the surface of the Earth.|thumbtime=0:02|thumb|Simulated views of the Moon over one month, demonstrating librations in latitude and [[longitude. Also visible are the different phases, and the variation in visual size caused by the variable distance from the Earth.]] thumb|Theoretical extent of visible lunar surface (in green) due to libration, compared to the extent of the visible lunar surface without libration (in yellow). The projection is the Winkel tripel projection|Winkel Tripel projection. [[Mare Orientale, just outside the yellow region, is brought into visibility from Earth by libration.]]
In lunar astronomy, libration is the cyclic variation in the apparent position of the Moon that is perceived by observers on the Earth 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. It is similar in both cause and effect to the changes in the Moon's apparent size because of changes in distance. It is caused by three mechanisms detailed below, two of which cause a relatively tiny physical libration via tidal forces exerted by the Earth. Such true librations are known as well for other moons with locked rotation.