Re: A rotating Earth?

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

The device Ptolemy used to account for the nonuniform rate of rotation
of epicycles about the deferent was called the equant.  It was the point
about which things moved at a uniform rate, but was not the center of
the deferent, so the rate of travel was non-uniform.  While I haven't
looked specifically for this, I am sure that Copernicus also had to rely
on the equant, so that for both Ptolemy and Copernicus the motion was
uniform about one point, and circular about others.  Far too messy for
the sort of idealism that Copernicus wanted.
I think there are some other factors too.  As opposed to most
astronomers of the time, Copernicus apparently was not an astrologer.
The core image of astrology is a geocentric world since the celestial
bodies focus on the earth...so for him recalling Hericlaetus was not
such a stretch.  Further, in the neoplatoic Christian tradition, the Sun
was the image of Christ, the source of all life...where do you suppose
that ought to be.

The story of why he did not publish is complicated..I'm not sure there is
general agreement about that...or that there could be.

cheers


On Fri, 4 Feb 2000, Digby Willard wrote:

> My understanding (still not from Kuhn...I don't have one) was that
> Copernicus developed his model primarily because he was offended by
> Ptolemy's departures from uniform circular motion.  That jibes with him
> being a neoplatonist, assuming that a neoplatonist is one who expects the
> universe to be perfect in a geometric way.  Ptolemy's model had everything
> moving in circles, but not everything moved uniformly.  In the Copernican
> model, everything went uniformly on circles.  As with Ptolemy's model,
> there were circles moving on circles moving on circles.  So Copernicus'
> model wasn't simpler, but it was more likely to satisfy his neoplatonic
> demand for geometric perfection.
>
> Also understood that Copernicus did not publish until he was close to
> death, and that historians were not certain he lived long enough to see a
> published copy of his work.  He was a priest, and I had thought that he had
> been afraid of the consequences of publication.  But maybe he wasn't
> satisfied with the results of his work, and only published when he realized
> he wasn't going to get anything better?
>
> I await comment, correction, clarification.
>
> Digby