Re: rotation of the earth
George Murphy (gmurphy@raex.com)
Fri, 12 Dec 1997 17:35:45 -0500gordon brown wrote:
>
> On Fri, 12 Dec 1997, Don Page wrote:
>
> > from the earth's rotation, which is small, but this came later.) The Greeks
> > noticed that the shadow of the earth on the moon during an eclipse was
> > round, but I have no idea as to whether this did or could have given much
> > evidence against the possibility of a highly prolate or oblate earth.
>
> Don,
>
> I believe that an additional part of the argument is that the shadow is
> always round no matter where the moon is in the sky, suggesting that all
> the earth's cross sections are circular.
The moon is always at (or very close to) one of the nodes of its
orbit relative to earth for an eclipse. But if the shadow is indeed
round for all eclipses, & thus for observers on all parts of the earth,
all its cross sections through its rotation axis are circles, so its
spherical. (Or do I need another step in there?)
George L. Murphy
gmurphy@imperium.net
http://www.imperium.net/~gmurphy