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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 modelECText/ch02_txt.htm#2.2.1.>.)
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/
brian whatcott <inet@intellisys.net>
Not according to NPR's "Math Guy" this morning:
<http://www.npr.org/ramfiles/wesat/20000219.wesat.04.ram>.
Larry
Altus OK