**The Astronomical Revolution and
the Rise of Modern Science**

Ancient Greek astronomy was founded by such pre-Socratic philosophers as
Empedocles, Anaximander, and Anaximenes, developed brilliantly by Plato,
Aristotle, and the mathematician Hypparchus, and reached its most systematic
expression in the *Almagest*, written in the second century CE by the
Alexandrian scientist, Ptolemy. The picture of the universe in Ptolemaic
astronomy has the earth at the center, with the sun, moon, and and the known
planets orbiting in circular paths around it. The so-called "fixed stars," which
do not seem to wander like the planets, are embedded in an outer, rotating
crystalline sphere. That outer celestial sphere is moved by being drawn to what
Aristotle called the "First" or "Unmoved" Mover. The celestial sphere in turn
communicates its motion to the sun, moon, and planets through an elaborate
gear-like system of "epicycles," which accounts for the irregular planetary
trajectories. Medieval Christianity inherited this picture of the universe from
the ancient Greeks, identifying the Unmoved Mover with the God of the Old and
New Testaments. The earth is at the center, since that is where the Garden of
Eden is created, where Adam and Eve sin, and where Christ redeems a fallen
humanity. Medieval Christianity even found a place for the angels in the region
between the outer celestial sphere and the Divine Unmoved Mover of the Ptolemaic
model. This is the conception of the universe that was overthrown by modern
science. In the 16th century, Copernicus, Kepler, and Galileo demonstrated that
the sun does not orbit the earth, but that the reverse is true: the sun is at
the center and the earth rotates around it. By so doing, they expelled humankind
from the center of the cosmos. They also forced us to recognize that ordinary
observation is not sufficient for science, since, after all, the sun does indeed
appear to circle the earth. As Galileo said, we must learn to read the book of
nature in the language in which it is written, the purely mathematical language
of circles, triangles, and squares. In the 17th century, Isaac Newton brought
this new mathematical and scientific conception of the world to systematic
expression in his masterwork, *Mathematical Principles of Natural Philosophy*.
In it used calculus, his own invention, to secure the foundations of
modern science by uncovering the fundamental equations, or laws, that govern the
motion of matter, both on the earth and in the heavens. With Newton's
achievement, modern science left philosophers with a new and extraordinarily
difficult task: to find a meaningful place for humankind in a universe that
appears to be operate according to purely mechanistic laws, and so to be
indifferent to our existence. - G. Zabel

**The Ancient and Medieval Conception of the Universe**

**Anaximenes**

**Aristotle**

**Ptolemy**

**Images of the Ptolemaic universe**

**Attempt to explain planetary motion, from Ptolemy's
Almagest**

**The Early Modern Picture of the Universe**

**Copernicus, and illustrations from his treatise, On Revolutions,
in which he advocated a heliocentric (sun-centered) view of the universe,
and ultimately overthrew the reigning Ptolemaic conception**

**Tycho Brahe, Astonomer of the Holy Roman Empire, and advocate
of a compromise between Ptolemy's and Copernicus' pictures of the cosmos**

**Brahe's compromise between Ptolemaic and Copernican astronomy**

**Johannes Kepler, mathematician, Imperial Astronomer, and
advocate of Copernican cosmology**

**Astronomical tables compiled by Kepler, and used to
demonstrate the validity of Copernicus' cosmological theory**

**Kepler's use of Plato's five regular solids to account for the
orbital paths of the planets around the sun**

**Giordano Bruno, advocate of Copernican astronomy and a
conception of the universe as infinitely extended in space and time**

**Bruno's treatise, On the Infinite Universe and Worlds**

**The infinity of the universe as understood on the basis of
Copernican cosmology**

**Bruno convicted of heresy by the Catholic Inquisition, and
burned at the stake**

**Galileo, the founder of modern mathematical physics**

**Galileo's telescope**

**Though Galileo did not invent the telescope, he was the first
to turn it to the sky, revolutionizing astronomy in the process**

**Galileo's treatise on the phases of the moon, and his sketch
of the moon's surface based on observations through the telescope**

**Galileo's drawing of sunspots. Along with his sketches of the
moon, it demonstrates, contrary to Ptolemaic and medieval belief, that the
heavenly bodies are "corruptible" material objects, and therefore the celestial
world is as imperfect as the earthly one.**

**Galileo's experiments with gravity, involving such instruments
as the pendulum and the leaning tower of Pizza, established the basis for
Newton's later systematic laws of motion.**

**Galileo called before the Catholic Inquisition by Cardinal
Bellarmine, on the orders of Pope Urban VIII. Unlike Giordano Bruno, Galileo
saved his life by publicly renouncing the Copernican theory. He was permitted to
live out the remainder of his life under the relatively mild conditions of house
arrest.**

**Isaac Newton, probably the most important scientist in history**

**William Blake's allegorical painting of Newton**

**Newton's Masterwork: Mathematical Principles of Natural
Philosophy**

**Newton's telescope. He extended the power of the Galilean
telescope enormously through the use of an additional lens.**

**Newton's Death Mask**