"David CL Francis" wrote in message
...
The real earth is not of course that flat except over the oceans!

Actually, as long as we're being pedantic, it's not even flat over the
oceans. It's much flatter, but the Earth simply is not an ideal "smooth
sphere" anywhere on its surface.

Also the further away you go the closer the horizon distance gets to being
the same as the height. It is obvious that from the moon you can almost
see the entire hemisphere.

Almost. But the difference is significant enough to matter when you
really care whether you can see the entire hemisphere (astronomy, for
example).