Librations of the Moon are revealed in these images. Due to the inclination of the Moon’s orbit and the fact that that it travels at varying speed throughout its eliptical orbit, the Moon appears to rotate and nod slightly over time. This is called libration and allows us to see about 59% of Moon, rather than the 50% that would be visible without libration.
The upper left image shows the crater Ptolemaeus visible at first quarter and at last quater during the same lunation. Without longitudinal libration it should be in one, but not both side of the terminator.
The upper right image shows images of the first and last quarter during a different lunation and reveals a nearly maximum latitudinal libration. They were joined at the crater Ptolemaeus to reveal just how much the Moon’s appearance changes. The lower left image shows the combined image centered on Ptolemaeus, which is just below the geographic center of the Earth-side of the Moon.
The lower right image summarizes the degrees of maximum libration in latitude and longitued.
© Eskildoodle 2021