SCIENTIFIC REVOLUTION 37
sub-orbits were carried around
the Sun. This system was best
refined by the great Greco-Roman
astronomer and geographer Ptolemy
of Alexandria in the 2nd century CE.
Even in the classical world,
however, there were differences
of opinion—the Greek thinker
Aristarchus of Samos, for instance,
used ingenious trigonometric
measurements to calculate the
relative distances of the Sun and
Moon in the 3rd century BCE. He
found that the Sun was huge, and
this inspired him to suggest that
the Sun was a more likely pivot
point for the motion of the cosmos.
However, the Ptolemaic system
ultimately won out over rival
theories, with far-reaching
implications. While the Roman
Empire dwindled in subsequent
centuries, the Christian Church
inherited many of its assumptions.
The idea that Earth was the center
of everything, and that man was
the pinnacle of God’s creation,
with dominion over Earth, became
a central tenet of Christianity and
held sway in Europe until the
16th century.
However, this does not mean
that astronomy stagnated for
a millennium and a half after
Ptolemy. The ability to accurately
predict the movements of the
planets was not only a scientific
and philosophical puzzle, but also
had supposed practical purposes
thanks to the superstitions of
astrology. Stargazers of all
persuasions had good reasonSee also: Zhang Heng 26–27 ■ Johannes Kepler 40–41 ■ Galileo Galilei 42–43 ■ William Herschel 86–87 ■
Edwin Hubble 236–41
Ptolemy’s model of the universe has Earth unmoving at the center,
with the Sun, Moon, and the five known planets following circular
orbits around it. To make their orbits agree with observations, Ptolemy
added smaller epicycles to each planet’s movement.
to attempt ever more accurate
measurements of the motions
of the planets.Arabic scholarship
The later centuries of the first
millennium corresponded with
the first great flowering of Arabic
science. The rapid spread of
Islam across the Middle East
and North Africa from the 7th
century brought Arab thinkers
into contact with classical texts,
including the astronomical
writings of Ptolemy and others.
The practice of “positional
astronomy”—calculating the
positions of heavenly bodies—
reached its apogee in Spain,
which had become a dynamic
melting pot of Islamic, Jewish,
and Christian thought. In the late
13th century, King Alfonso X of
Castile sponsored the compilation
of the Alfonsine Tables, which
combined new observations with
centuries of Islamic records to
bring new precision to the
Ptolemaic system and provide
the data that would be used to
calculate planetary positions
until the early 17th century.Questioning Ptolemy
However, by this point the
Ptolemaic model was becoming
absurdly complicated, with yet
more epicycles added to keep
prediction in line with observation.
In 1377, French philosopher
Nicole Oresme, Bishop of Lisieux,
addressed this problem head-on in
the work Livre du Ciel et du Monde
(Book of the Heavens and the
Earth). He demonstrated the lack
of observational proof that Earth
was static, and argued that there
was no reason to suppose that it ❯❯SaturnJupiterMarsEarth
MoonMercuryVenusSun