Resumo de New Astronomy - Astronomia Nova

Kepler was able to make so significant a contribution to
astronomy and physics because of the precise data he had
acquired from Tycho Brahe. Kepler was a Copernican and also
originally believed that the planets should follow
perfectly circular orbits. In fact, in Copernicus time the
state of the astronomical art in locating planets was
accurate to 10 ( 10 minutes of arc). With this level of
accuracy for the planets which could be measured the
circular orbit was acceptable. Brahe, however, made
measurements accurate to 2 of arc. Brahe had his own system
of the world, in which the earth was the center and the sun
revolved around the earth with the planets revolving about
the sun. In order to prove his system, or to settle between
the Copernican and Ptolemaic system he set out on precision
measurements of the locations of the planets. Brahe did not
use a telescope, so his method of observation was quickly
superseded by the telescopic investigations which began
about ten years after his death. Never the less, his
observations for 777 stars and the planet Mars have only
been fractionally improved today.
Tycho was a foul-
tempered Danish lord who tongue-lashed kings, tormented
peasants, sported a silver nose ( his own having been lost
in a youthful duel over mathematics), and kept a
clairvoyant dwarf as a court jester and a tame elk that got
drunk one night, fell down stairs, broke a leg and died.
Yet Tycho was a measuring maniac, a fussily precise man who
opened a new age of observation in science. ( p. 432)

Because of a disagreement with the new Danish King
Christian IV, he left his island observatory, Uraniborg and
went to Prague in 1597 to take up an appointment as
Imperial Mathematician for Rudolph II. In 1600 Kepler
joined Brahe. Kepler was a mystic who sought to develop
cosmology and he knew he needed access to Brahe's excellent
data. Brahe knew that Kepler was quite skilled in
mathematics and hoped Kepler would organize his data in a
useful form. Despite this mutual need it seems that Brahe
kept his data away from Kepler. About 1 1/2 years later
Brahe died from an acute urinary infection. His last words
to Kepler were, Let me not seem to have lived in vain."

Immediately after Brahe's death Kepler secretly took
away Brahe's data so that they would not be lost in the
settlement of Brahe's estate. Kepler was appointed to the
now vacant post of imperial mathematician. In 1627 Kepler
finally published a full set of tables that came from
Brahe's data called the Rudolphine Tables.
For six
years following Brahe's death Kepler was at war with the
planet Mars. Mars showed greater irregularities of motion
than the other planets. Kepler sought to find the curved
orbit around the sun that would describe Mars' orbit. This
was a daunting task since his observations were of a moving
body taken from a moving observatory( the earth). In his
book, Astronomia Nova, he describes the techniques he
devised to establish the orbit of Mars. Brahe's data,
collected over a period of some 25 years, was enough to
allow Kepler to determine twelve points on the orbit of
Mars. However, he could not force a circular orbit to go
through those points. Indeed, the orbit turned out to be
elliptical. The best circular orbit he could fit through
the data would have produced observational errors of 8' of
arc. Here the precision of Brahe's data was absolutely
crucial. Not only were these accurate data needed, but also
a conceptual break and high integrity on Kepler's part to
accept the data for what they said. A circular orbit for
Mars is out of the question. Kepler chose to believe the
observations, rather than the Platonic ideal of circular
motion. These observations were to be crucial for the
tests of Newton's theory of Universal Gravitation some
eighty years later.
I was almost driven to madness in
consideringating the matter. I could not find
out why the planet (Mars) would rather go on an elliptical
orbit.... With reasoning derived from physical principles
agreeing with experience, there is no figure left for the
orbit of the planet except for a perfect ellipse.... Why
should I mince words? The truth of Nature, which I had
rejected and chased away, returned by stealth through the
back door, disguising itself to be accepted....I thought
and searched, until I went nearly mad, for a reason why
the planet preferred an elliptical orbit.

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