The Moon

When you look at the full Moon, it looks like a flat disk. Why don’t you get a sense for its true three dimensions with your naked eyes? Relative to its distance from you—240,000 miles—the distance between your eyes is simply too small to produce a stereo effect. If your eyes were farther apart (say, 30,000 miles apart), you would see the Moon as it appears here: a sphere. Each dark area (mare) is an old impact basin where lava flowed long ago and solidified into dark basalt rock. The Moon is tidally locked with one face always pointed toward Earth. As the Moon orbits, the far side always points away from Earth, and we never see it. The far side was first photographed by the Soviet Luna 3 spacecraft in 1959, and first seen in person by the Apollo 8 astronauts when they rounded the Moon in 1968. Because the crust on the far side of the Moon is thicker than that on the near side, fewer basalt lava flows occurred when giant impacts occurred, and fewer mares were created.