Re: What would Sam have done?

On Tue, 20 Jan 2009 08:21:17 GMT, Troels Forchhammer
<Troels@xxxxxxxxxxxxxxxxxx> wrote:

In message <news:mji9n45a6628bfeglgmgs691qs2bjprdej@xxxxxxx>
Paul S. Person <psperson@xxxxxxxxxxxxxxxxxxxxxx> spoke these staves:


<snip>

However, it is certainly possible that, having the Copernican
system before him, Kepler was then able to make the leap from
circle to ellipse. I shall see when I reach that part of the
/Great Books of the Western World/.

Kepler had been a student with Tycho Brahe who had made some far more
precise measurements than what was available previously, which Kepler
inherited.

Brahe, sadly, is not in the Great Books of the Western World.

Brahe came up with a hybrid system, by the way, in which the earth
was in the centre still, the moon and the sun circled the earth, and
the rest of the planets circled the sun. From his measurements he
couldn't see a difference in star directions between summer and
winter, which meant that either the earth stood still, or the
distance from earth to the nearest star would have to be at least a
thousand (IIRC) times the distance between earth and sun, and Brahe
didn't believe that God would have been so lavish with space in the
universe.

That stirs a vague memory; I think I have read about Brahe before.

Ptolemy, incidentally, demonstrates in his first book that the Earth
is a dimensionless point in relation to the rest of the Universe (ie,
the sphere of fixed stars).

Of course, he also proves that the Earth is in the exact center of
that same sphere of fixed stars. The argument as such makes sense; the
problem, of course, is that there is no sphere of fixed stars in
reality.

Kepler, either because he had more time or because he was a better
mathematiciam (or both), used the differences between the predictions
of the circular model and Brahe's measurements to come up with the
ellipses and the three laws (he probably also had older data for
control, but Brahe's data was of better quality).

Incidentally Brahe was also the one to observe a supernova (Stella
Nova) which violated another principle in the Aristotelian world-
view: that of the immutability of the crystal spheres.

By Brahe's day the spheres may have been crystal, but I don't recall
anything in Aristotle, Ptolemy, Aquinas, Dante, or Copernicus that
clearly said they were. I may have overlooked something, of course; or
I may have misunderstood a reference which would be clear if it were
pointed out; or it may have been an underlying assumption that was
never clearly stated.

Actually, I recall being surprised not to notice it in Copernicus.

Aristotle, of course, taught that the heavenly bodies, being composed
of the fifth element (the "quintessence", to use the Latin form), were
incorruptible and so immutable, so Brahe's Stella Nova would
definitely have called that into question. The discovery that the Moon
and the planets were ordinary matter, composed of the same four
elements as the Earth, was a blow to Aristotlean physics for the same
reason. As was the replacement of all those perfect circles (the
heavenly bodies can only move in perfect circles because otherwise
their motion would undergo change, and so they would undergo change,
which incorruptible and immutable beings cannot do) with ellipses.

Oh -- and I forgot to mention that Brahe was a Danish noble who made
his measurements from his observatory on the island Hven in the sound
between (now) Denmark and Sweden ;-)
--
Here lies the Tuscan poet Aretino,
Who evil spoke of everyone but God,
Giving as his excuse, "I never knew him."
.

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