There are a few ideas i've come across.

One is that there is an energy source beneath the world which effectively penetrates it and "draws" the "xray" in ionized air high above.

Some couple this with the "crater earth" idea, where the earth we know is only (within) one small crater depicted on the moons surface.

Interestingly enough, this is somewhat consistent with the biblical conception of the world, where it is described as if a seal pressed into wax (aka, a crater).