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Re: Copernican Revolution



Copernicus' total system was about as accurate as Ptolemy's and had about
as many epicycles.

HOWEVER, the simplified Copernican system with NO epicycles is much more
accurate (i.e, predicts the retrograde motion of planets) than the
Ptolemaic system with no epicycles.

Richard Grandy
Center for the Study of Science and Technology
Rice Unversity
Houston TX




At 4:01 PM -0600 2/19/00, brian whatcott wrote:
Copernicus points out an immediate difficulty of the epicyclic model
for Venus early in book 1 of De Revolutionibus - a matter of the
varying apparent diameter of that planet needed to comply with a
Ptolomeian epicycle.
(And Osiander's Introduction to the work mentions it on page 1.)

In Book three, while describing a circular orbit for Earth, he
attempts to resolve the variability of the annual circuit by placing
the Sun eccentric (closer to a focus of an ellipse, as we would say).

"But whatever things take place by means of the epicycle can happen
in the same way by means of the eccentric circle..."

He frequently compares and contrasts an epicyclical model with an
eccentric model, and at times displays a quite modern sense of
suspended judgment as to what the actual cause of the orbital
irregularities shall be.

Brian W

At 13:14 2/19/00 -0700, you wrote:
Historical question: I thought Copernicus' heliocentric model
was not initially any more accurate than Ptolemy's.
Didn't he even have to have a
few epicycles himself? Until Kepler? (See
<http://www.physics.gmu.edu/classinfo/astr103/CourseNotes/
ECText/ch02_txt.htm#2.2.1.>.)

Not according to NPR's "Math Guy" this morning:
<http://www.npr.org/ramfiles/wesat/20000219.wesat.04.ram>.

Larry


brian whatcott <inet@intellisys.net>
Altus OK