Why cant the whole moon be seen from earth?

A2. The Moon keeps one side locked towards Earth. Thus whether it were illuminated or not, we can never see the far side of the Moon.

Incidentally, there is a marvellous movie of the complete Lunar cycle under Moon/Tidal effects in Wikipedia.

A1. The sun casts a light on one side of the moon and the other side is a dark shadow. So if there is a half moon, for example, from earth, we can see half of the lighted side and half of the dark side, which makes it look like the moon is cut in half. Since the Earth rotates, we can see a different side every night, and that's how we can see more or less of the lighted side of the moon. For a new moon, Earth can see the whole dark side and none of the lighted side. For a full moon, Earth can see the whole lighted side and none of the dark side.