De Revolutionibus Orbium Coelestium
On the Revolutions of the Heavenly Spheres
- Polish, studied in Cracow
- studied in Italy for ten years (law, mathematics, medicine)
- returned to Cracow as a cleric
- worked on manuscript about motions of the planets
- decided to publish at urging astronomer friend Rheticus
- saw the proofs on his deathbead
He put the sun at the center of
the Copernican system ,
in contrast to the the Ptolemaic system
- Predictions obtained with the Ptolemaic system
did not quite match observations.
[others have considered that the earth moved, even though that
"... I considered that I too might well be allowed to try whether
sounder demonstrations of the revolutions of the heavenly orbs might
be discovered by supposing some motion of the earth ... I found after
much and long observation, that if the motions of the other planets
were added to the motions of the earth, ... not only did the apparent
behavior of the others follow from this, but the system so connects the
orders and sizes of the planets and their orbits, and of the whole
heaven, that no single feature can be altered without confusion among
the other parts and in all the Universe. For this reason, therefore,...
have I followed this system."
- "In this orderly arrangement there appears a wonderful symmetry in
the universe and a precise relation between the motions and sizes
of the orbs which is impossible to obtain in any other way."
- In contrast, the Ptolemaic system is complicated, especially
with its equants.
"...the planetary theories of Ptolemy and most other astronomers, although
consistent with the numerical data, seemed... to present no small
difficulty. For these theories were not adequate unless certain equants were
also conceived; it then appeared that a planet moved with uniform velocity
neither on its deferent nor about the center of its epicycle. Hence a
system of this sort seemed neither sufficiently absolute nor sufficiently
pleasing to the mind."
- Still... to get the motions just right, Copernicus needed some
small epicycles and spheres not centered exactly on the sun.
Response of the readers: some liked it, some didn't. The Catholic
Church didn't, and placed it on the Index Expurgatorius.
Why? Remember Luther (1517). The church had serious problems and could
see new ideas as dangerous.
ASTR 121 Home
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA