# Collier's New Encyclopedia (1921)/Kepler, Johann

**KEPLER**, or **KEPPLER, JOHANN**,
a German astronomer; born in Weil der
Stadt, Wiirttemberg, Dec. 27, 1571. He
was left to his own resources when a
mere child, his education depending on
his admission into the convent of
Maulbronn. He afterward studied at the
University of Tübingen, applying himself
chiefly to mathematics and astronomy.
In 1593 he was appointed Professor of
Mathematics at Gratz, and about 1596
began a correspondence with Tycho
Brahé, went to Prague, where he lived
for 11 years in great poverty. He then
obtained a mathematical appointment at
Linz, and 15 years afterward was
removed to the University of Rostock. In
his “Mystery” (1596), he proclaims that
five kinds of regular polyhedral bodies
govern the five planetary orbits. At
length convinced that this theory was
only an error, after 22 years of patient
study he was able at last to announce in
his “Harmonies of the World” (1619)
that the “square of a planet's periodic
time is proportional to the cube of its
mean distance from the sun.&lrquo; This rule
is known as Kepler's Third Law. Finding
the theory of epicycles unable to bear
the strain of Tycho Brahe's accurate
observations, especially in the case of the
planet Mars, he endeavored to find a law
for the planet's movements which would
be simple and satisfactory. After enormous
labor, and by a process of trial and
error, he found that (1) the planet's
orbit was an ellipse, of which the sun is
one focus, and (2) that, as the planet
describes its orbit, its radius vector
traverses equal areas in equal times. These
rules (published in 1609 in his work on
“The Motions of Mars”) are known as
Kepler's First and Second Laws respectively.
These laws formed the ground-work
of Newton's discoveries, and are
the starting-point of modern astronomy.
Besides, we owe to Kepler many discoveries
in optics, general physics, and
geometry. He died in Ratisbon, Nov. 15,
1630.