Washington, June 21 -- Despite the name of Pink Floyd's best-selling album, the side of the moon you can't see isn't always dark. But it is far.

So scientists call the area where a Chinese spacecraft just landed the far side, not the dark side.

"The other side sees the sun sometimes. The other side is not dark, it's just far," said Harvard astronomer Avi Loeb. "It's a mistake."

The moon is what scientists call "tidally locked " which means the same side always faces us, while another side always faces away, Loeb said. When Earth views a darkened new moon, the far side is lit. When there's a full moon in our sky, the far side is dark.

Every semester, Purdue University lunar and planetary scientist Jay Melosh demonstrates how the far si...