i did a load of research on theories about the moon for an english project and read some stuff about how the may be moon hollow. (this is only beleivable if you think people did go to the moon). when apolo XII landed on the moon they drilled down into the surface and set up seismometers to measure seismic activity on the moon. as the astronauts left the moon the ditched the ascent stage of the lunar module, which fell to the moons surface. when these landed the seismometers piked up reverberations through the moon. this would sujest that the moon was hollow.