II. Towards a sun-centered perspective
A. The men of transition: The Renaissance Natural
Philosophers
COPERNICUS (1473-1543)
A contemporary of Michaelangelo and an amateur astronomer, Copernicus
was born in Poland and studied at the University of Cracow till 1494. In
1496 he goes to Italy to study law in Bologna and theology and medicine
in Padua. In 1506 he went back to Poland and assumed the post of canon
at the cathedral of Frauenburg, a clerical post he would hold for the rest
of his life. He also set up an observatory.
As a result of his observations, he came to realize that the actual
positions of the planets did not match their positions predicted by the
geocentric (ptolemaic) model, and that therefore, the Ptolemaic and Aristotelian
systems were inadequate. This led him to change the geocentric system that
had been evolved over millennia, and whose basics matched our everyday
experience to a heliocentric (sun-centered) system. In his new system,
it is no longer the earth, but the sun that is at the center of the universe,
and the moon becomes a satellite of the earth. All six planets, (now including
the earth) go around the sun. From the ancients he retains circular orbits.
Unfortunately, these circular orbits did not prove to be better predictors
of planetary orbits than those of Ptolemy.
In 1530 he wrote a summary of his views in Commentariolus,
a book that was well received by scholars and clergy alike. One supporter
in particular was pope Clement VII. The full account of his work was finally
published in De Revolutionibus Orbium Coelestium in 1543, and supposedly
it was presented to him on his deathbed.
While observations did play a part in Copernicus' rejection of the
Ptolemaic model, it should be emphasized that the new system was based
on philosophical and aesthetic motivations. His system, like those of the
astronomers that came before him, had to fit what the naked eye saw. Copernicus'
system also had to please the mind, to fit the basic axioms of physics,
namely that all motion is uniform and circular. In his opinion, he evolved
this new system to return order, simplicity and mathematical harmony to
the world of astronomy.
It must also be mentioned that Copernicus’ new cosmology was not
challenged by the church. At that time, the church had no official astronomical
dogma and, his works were commonly read in catholic universities.
TYCHO BRAHE (1546-1601)
The son of a rich Danish nobleman, Brahe would pursue his passion
for astronomical observation his entire life. In 1572 he observed a new
star, a nova (actually an exploding star). According to Aristotle, novae
happen between the Earth and the Moon. Careful observation showed Brahe
that Aristotle was wrong and that this object was celestial, not sub-lunar
in nature.
In 1576 the Danish king, Fredrick II, granted Brahe an island in
the North Sea (Hveen) where he constructed two observatories from where
he would conduct careful observations and accumulate more astronomical
facts than anyone before him. At Hveen, he observed several comets and
was able to prove that comets are celestial objects, not atmospheric phenomena
as Aristotle had claimed. Brahe noted that the paths of these comets clearly
cut across the paths of the planets. If the heavens were made of nested
crystalline spheres, as many ancient astronomers, including Aristotle,
had thought, the comets would have collided with these spheres, therefore
Aristotle, Ptolemy and the ancients were wrong.
To Brahe, Copernicus was not right either. If the earth moved, Brahe
should be able to detect parallax which he could not do. Thus in an attempt
to reconcile the problems between his observations and the Ptolemaic and
Copernican models he proposed his own system. Brahe's system was a modified
geocentric model, with an unmoving earth at the center, and the other planets
going around a sun that moved around the earth.
In 1588, with the death of Fredrick II, and the lack of support from
his successor, Christian IV, Brahe leaves Denmark to become Court Mathematician
to the Emperor Rudolph II in Prague. There, his main task was to prepare
and publish the Rudolphine tables, tables of astronomical positions. It
is a task he himself would never complete, as he dies in 1601; but they
would be completed 26 years after his death by his assistant Johannes Kepler.
What makes Brahe so important in the history of astronomy is that
he was a superb observational astronomer, undoubtedly the best before the
use of telescopes, and that he kept detailed records of his observations
for a span of nearly 40 years. It was left to his assistant, Johannes Kepler,
who fell heir to Brahe’s data, to actually figure out the true motions
of the solar system. |