Selenology: Snapping the Hidden Face

As every sky-gazer knows, only one face of the moon is visible. Terrestrial gravity has locked onto the moon's near side, which always faces the earth. Some scientists have theorized that the hidden side bore many more craters and pockmarks than the visible face. That concept was first shaken by Lunar Orbiter 4, which mapped some 60% of the far side. Last week, Lunar Orbiter 5 knocked the notion completely into a cocked hat while completing the map.

What Lunar Orbiter 5's strikingly clear wide-angle and telephoto pictures show, according to NASA scientists,...

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