Christopher M. Jones wrote:

That's not the half of it. Think about the troubles of
navigation. For millenia it was difficult to determine
both longitude and latitude on the open ocean. Latitude
was the easiest to determine with crude methods (height
of the Sun above the horizon at noon, etc.) and
travelling along one partituclar line of latitude was
the easiest form of oceanic navigation for a long time.
But having a gigantic planet in the sky adds a new twist.
Just look up and you can see what time it is at 0
longitude, plus, you can just look at the position in
the sky of the planet and know what your position on the
moon is fairly easily. That would make early map making
and long distance travel a lot easier.




On the half of the planet facing the moon, yes...but the people on the
far side would still have navigation problems....on the upside, having
such an object in the sky at noting it's changing position as one
traveled would make the fact that you were living on a sphere (Okay...a
bit of an ellipsoidal sphere maybe) fairly obvious at an early phase of
civilization.
Pat