To all,
Just a couple of notes on this discussion. First Tycho's theory was very
popular from when it was proposed until at least 1620's. The reason being
that it allow one to keep Aristotelian physics while using what is a
similar mathematical model to the Copernican one. Only the position of the
Sun and the Earth are reversed. One of the chief advantages of the
Copernican model is that it easier to perform some of the planetary
position calculations even though it is argumentatively more complex
geometrically. This ease of computations meant that many astronomers who
didn't believe it used it to calculate positions.
As Aristotle argues the earth cannot rotate once a day since if it did
there would be great winds when you step outside. Copernicus avoided this
whole issue. In fact this is one of greatest services that Copernicus did
for science. He separated Aristotelian physics from astronomy. This allowed
both to be attacked independently.
For years scientific historians though that Tycho's Universe was just an
interesting footnote. Being far more complicated and intellectually
cumbersome then Copernicus', that is until they started looking into the
scientific response to Galileo's arguments for the Copernican Theory. As
Kepler and others point out, these observations are consistent with either
the Copernican or Tychonic models. A point that Galileo just ignores.
Brahe turned Kepler loose on the orbit of Mars which is the most
elliptical one of the well observed planets. Mercury is more elliptical but
much harder to observe. The orbital calculations differed only 7 minutes of
arc from the true position of Mars, and for these 7 minutes he threw out
all that had gone before. If Tycho was accurate to another significant
figure he would have detected the deviations from the Keplerian system
caused by perturbations of the planets.
Another tenet of Aristotle's model is that the planets moved in uniform
circular motion, and it was only Kepler's second law that motivated an
abandonment of this idea.
The incorrectness of the Tychonic model was shown by Bradley's observation
of the aberration of star light. A hundred and fifty years after Tycho
proposed it. By this time it had of course been superseded by Kepler's model.
Gary
Gary Karshner
St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU