Kempeneer, Pieter de See CAMPANA, PEDRO DE
Kepler, Johannes (1571–1630) German astronomer
Born near Wittenberg, the son of a mercenary, Kepler was
educated at Tübingen university where, as a student of
Michael MAESTLIN, he was introduced to astronomy and
became an early convert to the COPERNICAN SYSTEM. Here
also he began to consider the problem of why there were
only six planets (according to the contemporary count)
and why they were sited in their particular orbits. In his
Mysterium cosmographicum (1596) he proposed that God
had modeled the universe on the pattern of the five regu-
lar solids of 4, 6, 8, 12, and 20 sides respectively. Before he
could advance further, he realized, he would need fuller
and more accurate data.
Access to such data came in 1599 when he was in-
vited by Tycho BRAHE, the leading observer of his day, to
join him at his Prague observatory. The death of Brahe
soon afterwards (1601) left Kepler in charge of all his ob-
servations. With them Kepler was able to reshape astron-
omy. After several years’ struggling to make sense of the
orbit of Mars, Kepler finally saw in 1605 that planetary or-
bits were elliptical, not circular as had previously been
thought. This result, since known as Kepler’s first law, was
revealed in his Astronomia nova (1609). The debt to Brahe
was repaid after many years with the publication of his ob-
servations in 1627 as the Tabulae Rudolphinae (the
Rudolfine Tables, so called after Brahe’s and Kepler’s pa-
tron Emperor RUDOLF II). Ever convinced, however, that
the universe was built to some divine design, Kepler con-
tinued to search for the key to the cosmic mystery. His
final thoughts on the matter were contained in his Har-
monices mundi (1619), a work in which he also first for-
mulated his third law. His Epitome astronomiae Coperni-
canae (1618–21), which was the first manual of astron-
omy to be based on the Copernican system incorporating
Kepler’s own laws of planetary motion, was placed on the
INDEX LIBRORUM PROHIBITORUMin 1619, after the publica-
tion of the first three books.
Kepler’s personal life was to prove less successful. Al-
though he succeeded Brahe in 1601 as imperial math-
ematician to Rudolf II he found the duties irksome and
often unpaid. In 1612 he moved to Linz as provincial
mathematician. The outbreak of the Thirty Years’ War in
1618, religious controversies, domestic troubles, and the
need to defend his mother against a charge of witchcraft,
together with a perennial shortage of funds, ill health, and
intense intellectual labors, made the latter part of Kepler’s
life both hectic and unpredictable. After abandoning Linz
in 1627, he settled in Silesia in 1628 in the service of the
statesman and general Wallenstein. He died at Regens-
burg, while traveling to Linz to collect a debt.
See also: ASTRONOMY
Further reading: Max Caspar, Johannes Kepler, transl.
C. Doris Hellman (New York: Dover, repr. 1993); Kitty
Ferguson, Tycho and Kepler (New York: Walker, 2002);
James R. Voelkel, Johannes Kepler and the New Astronomy
(Oxford, U.K.: Oxford University Press, 2001); ∼The
Composition of Kepler’s Astronomia nova (Princeton, N.J.:
Princeton University Press, 2001).
Key, Lieven de (1560–1627) Netherlands stonemason and
architect
Key was born in Ghent and after working in England for
some years moved to Haarlem (1591), where he remained
for the rest of his life. His highly ornamental style was
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