cosmology with the sun at the centre of the universe.
Copernicus (1473-1543) is the first modern to suggest that the earth moves round
a central sun (heliocentrism) rather than the
sun moves around a central earth (geocentrism),
with the publication of De Revolutionibus in
1543. However, the reception of this theory is surprisingly muted. It was
certainly not accepted immediately, as there are too many problems and too few
advantages. Not until Kepler and Galileo is it taken as a serious challenge, in
cosmological terms, to the Ptolemaic system. It is seen to be useful by
astronomers for simpler methods of predicting the motions of the heavens.
Kepler (1571-1630) greatly simplifies the new cosmology by showing that the
planetary orbits are in fact simple ellipses around the sun (discovered 1605,
published 1609). He is the first to break with Platos idea of regular
Galilei (1564-1642) is the first to make systematic use of the telescope
(1609/10 on), and finds a great deal of evidence against the old system, and
some evidence in favour of the new. He also does important work in producing new
theories of motion which do away with many important objections to the
heliocentric system, based on Aristotles views.
Newton (1642-1727) finally cements this revolution with the 1/d2
gravitational law, which gives a proper explanation of the elliptical orbits of
the planets, and of motion on the earth.
all, it is important to recognise that the Copernican system was not
significantly more accurate than the Ptolemaic system it replaced. However, it
is a more elegant explanation of retrogression, as due to relative motion of
earth and planets. There is a proper ordering of planets and estimation of
planetary distances, for example it yields as explanation of why Mercury and
Venus are always seen near sun. The real improvement is its simplicity - instead
of those fearsome Ptolemaic devices for the apparent motions of the planets, and
in particular retrogressions, we have simple orbits around the sun.
by: Richard P Whaite
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