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Kepler
Kepler's univers
Kepler, Johannes (1571-1630), German
astronomer and natural philosopher, noted for formulating and
verifying the three laws of planetary motion. These laws are now
known as Kepler's laws.
Kepler was born on December 27, 1571, in
Weil der Stadt in Württemberg and studied theology and classics
at the University of Tübingen. There he was influenced by a
mathematics professor, Michael Maestlin, an adherent Of the
heliocentric theory of planetary motion first developed by the
Polish astronomer Nicolaus Copernicus. Kepler accepted Copernican
theory immediately, believing that the simplicity of Copernican
planetary ordering must have been God's plan. In 1594, when
Kepler left Tübingen for Graz, Austria, he worked out a complex
geometric hypothesis to account for distances between the
planetary orbits—orbits that he mistakenly assumed were
circular. (Kepler later deduced that planetary orbits are
elliptic; nevertheless, these preliminary calculations agreed
with observations to within 5 percent.) Kepler then proposed that
the sun emits a force that diminishes inversely with distance and
pushes the planets around in their orbits. Kepler published his
account in a treatise entitled Mysterium Cosmographicum
(Cosmographic Mystery) in 1596. This work is significant because
it presented the first comprehensive and cogent account of the
geometrical advantages of Copernican theory.
Kepler held the chair of astronomy and
mathematics at the University of Graz from 1594 until 1600, when
he became assistant to the Danish astronomer Tycho Brahe in the
latter's observatory near Prague. On the death of Brahe in 1601,
Kepler assumed his position as imperial mathematician and court
astronomer to Rudolf II, Holy Roman emperor. One of his major
works during this period was Astronomia Nova (New Astronomy,
1609), the great culmination of his painstaking efforts to
calculate the orbit of Mars. This treatise contains statements of
two of Kepler's so-called laws of planetary motion. The first is
that the planets move in elliptic orbits with the sun at one
focus; the second, or “area rule,” states that a
hypothetical line from the sun to a planet sweeps out equal areas
of an ellipse during equal intervals of time; in other words, the
closer a planet comes to the sun, the more rapidly it moves.
In 1612 Kepler became mathematician to
the states of Upper Austria. While living in Linz, he published
his Harmonice Mundi (Harmony of the World, 1619), the final
section of which contained another discovery about planetary
motion: The ratio of the cube of a planet's distance from the sun
and the square of the planet's orbital period is a constant and
is the same for all planets.
At about the same time he began
publishing a book that took three years to appear, the Epitome
Astronomiae Copernicanae (Epitome of Copernican Astronomy,
1618-21), which brought all of Kepler's discoveries together in a
single volume. Equally important, it became the first textbook of
astronomy to be based on Copernican principles, and for the next
three decades it was a major influence in converting many
astronomers to Keplerian Copernicanism.
The last major work to appear in
Kepler's lifetime was the Tabulae Rudolfinae (Rudolfine Tables,
1625). Based on Brahe's data, the new tables of planetary motion
reduced the mean errors from 5° to within 10’ of the actual
position of a planet. The English mathematician Sir Isaac Newton
relied heavily on Kepler's theories and observations in
formulating his theory of gravitational force.
Kepler also made contributions in the
field of optics and developed a system of infinitesimals in
mathematics, which was a forerunner of calculus.
Kepler died on November 15, 1630, in
Regensburg.
( Ptolemy - Copernicus - Kepler - Galileo - Newton )
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Copyright JoaoVicente.
Last update: 11/02/98.
