mare orientale

Were it not for its position, largely hidden beyond the western limb, this would be the most dramatic lunar feature visible. It is the result of the collision of an asteroid-sized body some 3 billion years ago. As seen here from the Lunar Orbiter in 1967, the three concentric mountainous walls thrown up by the impact are reminiscent of a huge eyeball.

Photo: NASA, Lunar Orbiter 4.

Inconstant Moon