= Libration
{wiki}
<Libration> is the apparent rocking of a body as seen by an observer. For the <Moon>, longitudinal <libration> arises because <orbital eccentricity> makes its orbital angular speed vary while its spin is much more uniform: the direction to <Earth> advances ahead of, then falls behind, the mean facing direction. The <Moon>'s tilted geometry also causes latitudinal <libration>; small actual rotational oscillations provide further corrections. Thus lunar <synchronous rotation> holds in the mean, rather than requiring exact instantaneous alignment. https://svs.gsfc.nasa.gov/5195/[NASA Scientific Visualization Studio: libration in longitude]{ref}. https://svs.gsfc.nasa.gov/5588/[NASA Scientific Visualization Studio: lunar phase and libration]{ref}.
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