Earth's Libration Visualized For the First Time Above the Moon's Far Side 33
StartsWithABang writes Thanks to the fact that the Moon is tidally locked, we can only see 50% of its surface on any given night. Over time, the fact that the Moon's orbit is elliptical, and that it moves faster at perigee and slower at apogee means that up to another 9% is visible over the course of many years. The observed "rocking" and growing/shrinking of the Moon over time is known as lunar libration, an incredibly interesting phenomenon. But now, for the first time, we've been able to visualize how the Earth appears to move as seen from above the far side of the Moon.