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Arabic and Indian astronomers.
Supporters of geocentrism rejected
his idea as absurd, believing a
spinning Earth would create huge
winds, such that objects on Earth’s
surface would simply fly off.
Another idea, first proposed by
Aristarchus of Samos in about
250 bce, was that Earth might
move around the sun. Not only did
this go against deeply ingrained
Aristotelian ideas, but supporters of
geocentrism had also for centuries
cited what seemed a scientifically
valid reason for ruling it out—the
“lack of stellar parallax.” They
argued that if Earth moved around
the sun, it would be possible to
observe some variation in the
relative positions of stars. No such
variation could ever be detected
so, they said, Earth could not move.THE COPERNICAN MODEL
In his 1660 star atlas, German
mapmaker Andreas Cellarius illustrated
the cosmic systems of Ptolemy, Tycho
Brahe, and Copernicus (shown here).
All three still had their champions.In the face of such an established
philosophical tradition with
little observational evidence to
contradict it, and the theological
arguments in favor of it, the
geocentric view of the universe
went unchallenged for centuries.
However, in about 1545, rumors
began circulating in Europe of a
highly convincing challenge that
had appeared in the form of a book
entitled De revolutionibus orbium
coelestium (On the Revolutions of
the Celestial Spheres), by a Polish
scholar, Nicolaus Copernicus.Copernican revolution
The work was extremely
comprehensive, and proposed
a new, detailed, mathematical,
and geometrical model of how the
universe works, based on years
of astronomical observations.
Copernicus’s theory was based
on a number of basic propositions.
First, Earth rotates on its axis daily,
and this rotation accounts for most
of the daily movements of the stars,
sun, and planets across the sky.Place the sun himself at
the center of the universe.Ptolemy’s Earth-
centered model of the
universe relies upon
complex adjustments to
explain observed data.Copernicus’s
sun-centered model
explains the same data
with far fewer
adjustments.Copernicus believes
his model is more
elegant, and thus more
likely to be correct.