Johannes Kepler was the first to apply the new
mathematics to divine the laws
of celestial motion. Kepler adopted a Copernican, heliocentric view of the
universe from his earliest days. He focused on the number, size, and relation
of the planets, seeking some grand design. After years of calculations and
attempts to fill the gaps in his theories, he finally created a model of the
universe that satisfied him. He noted that there were six known planets, thus
five intervals between them, and noted that there were five possible regular
solid figures (that is, figures with equal sides and angles)--cubes,
tetrahedrons, dodecahedrons, icosahedrons, and octahedrons. By layering these
solid figures, one inscribed within the next, in this order from largest to
smallest, he believed he could map the orbits of the planets. This scheme was
soon discredited, but Kepler continued to search for some divine plan,
explicable by simple mathematics, to explain the structure of the universe.
In 1609, Kepler published New Astronomy with Commentaries on the Motions of
Mars. The work clearly sets forth two of the tenets of modern astronomy: 1)
the planets move around the sun not in circles, but ellipses; 2) planets do not
move uniformly, but in such a manner that a line drawn from a planet to the sun
sweeps out an equal area of the ellipse of its orbit in equal time, even if the
ellipse is not perfectly centered on the sun. In 1618, Kepler presented the
third of his laws of planetary motion, stating that the squares of the
periods of the planets' orbits are proportional to the cubes of their distances
from the sun. These observations were all at least somewhat accurate, and led
to the final discarding of Aristotelian cosmology by the academic world.
Galileo Galilei was the most well known and successful scientist of the
Scientific Revolution, save Isaac Newton. In 1604, by observing the
appearance of a new luminous body in the remote region of space for which no
motion of the stars could be detected, he demonstrated that the remote and,
according to Aristotelian cosmology, static region of space was not actually
static. In 1609, Galileo introduced both the telescope and the microscope. His
first observations with the telescope were published in 1610, in a 24-page
booklet entitled Messenger of the Heavens. The first half of the booklet
described Galileo's observation of the surface of the moon, which he proved was
rough rather than smooth. He professed the existence of up to ten times as many
distant, seemingly fixed stars than were currently known. The second half of
the book is largely devoted to the moons of Jupiter.
In 1612, Galileo announced that through the observation of dark spots on the
sun, he had concluded that the sun itself was revolving. This announcement
spawned one of his first conflicts with the Church, which considered these
findings contrary to Church doctrine. In 1616, the Inquisition warned
Galileo to "abandon these opinions." A few days later, the works of Copernicus
were "suspended till corrected."
By 1630 Galileo had completed his magnum opus, Dialogue on the Two Chief
Systems of the World, comparing the Ptolemaic, or geocentric and the
Copernican, or heliocentric systems, and finding the heliocentric model far
superior. In the work Galileo discussed at length the doctrine of
uniformity, proposing the view that corresponding causes produce corresponding
affects throughout the universe, thus leading to the recognition that
terrestrial physics may be used to explain the motion of heavenly bodies. This
philosophy was in direct opposition to the Church-sponsored Aristotelian
system, which aligned itself with a geocentric view of the universe and
differentiated between terrestrial and celestial physics.
The Dialogue brought matters to a head for Galileo. In August 1632 the
sale of the book was prohibited, and its contents examined by a special
commission. Galileo was found guilty of heresy and forced to sign a recantation
of his theories, after which he was sentenced to house arrest for the remainder
of his life. Galileo signed the recantation to save his own life, but legend
has it that as he signed the prepared document, under his breath he muttered
"the Earth does move, however."
