The Solar System

CHAPTER 4 | THE ORIGIN OF MODERN ASTRONOMY 63

a luxurious home with six towers especially equipped for astron-
omy and populated it with servants, assistants, and a dwarf to act
as jester. Soon Hveen was an international center of astronomical
study.

Tycho Brahe’s Legacy

Tycho made no direct contribution to astronomical theory.
Because he could measure no parallax for the stars, he concluded
that Earth had to be stationary, thus rejecting the Copernican
hypothesis. However, he also rejected the Ptolemaic model
because of its inaccuracy. Instead he devised a complex model in
which Earth was the immobile center of the universe around
which the sun and moon moved. Th e other planets circled the
sun (Figure 4-11). Th e model thus incorporated part of the
Copernican model, but in it Earth—not the sun—was station-
ary. In this way, Tycho preserved the central immobile Earth.
Although Tycho’s model was very popular at fi rst, the Copernican
model replaced it within a century. Th e true value of Tycho’s
work was observational. Because he was able to devise new and
better instruments, he was able to make highly accurate observa-
tions of the position of the stars, sun, moon, and planets. Tycho
had no telescopes—they were not invented until the next
century—so his observations were made by the unaided eye peer-
ing along sight-lines. He and his assistants made precise observa-
tions for 20 years at Hveen.

Unhappily for Tycho, King Fredrik II died in 1588, and his

young son took the throne. Suddenly, Tycho’s temper, vanity, and

noble presumptions threw him out of favor. In 1596, taking

most of his instruments and books of observations, he went to

Prague, the capital of Bohemia, and became imperial mathemati-

cian to the Holy Roman Emperor Rudolph II. His goal was to

revise the Alfonsine Tables and publish the result as a monument

to his new patron. It would be called the Rudolphine Tables.

Tycho did not intend to base the Rudolphine Tables on the

Ptolemaic system but rather on his own Tyconic system, proving

once and for all the validity of his hypothesis. To assist him, he

hired a few mathematicians and astronomers, including one

Johannes Kepler. Th en, in November 1601, Tycho collapsed at a

nobleman’s home. Before he died, 11 days later, he asked Rudolph

II to make Kepler imperial mathematician. Th e newcomer became

Tycho’s replacement (though at one-sixth Tycho’s salary).

Kepler: An Astronomer of Humble

Origins

No one could have been more diff erent from Tycho Brahe than

Johannes Kepler (■ Figure 4-13). Kepler was born in 1571 to a poor

family in a region that is now part of southwest Germany. His

father was unreliable and shiftless, principally employed as a merce-

nary soldier fi ghting for whoever paid enough. He was often absent

for long periods and fi nally failed to return from a military

The Five Regular Solids

Cube

Tetrahedron

Sphere

of Mars

Sphere of Jupiter

Sphere of Saturn

Epicycle

of Saturn

Epicycle

of Jupiter

■ Figure 4-13

Johannes Kepler (1571–1630) was Tycho Brahe’s successor. This diagram,
based on one drawn by Kepler, shows how he believed the sizes of the celes-
tial spheres carrying the outer three planets—Saturn, Jupiter, and Mars—are
determined by spacers (blue) consisting of two of the fi ve regular solids.
Inside the sphere of Mars, the remaining regular solids separate the spheres
of the Earth, Venus, and Mercury (not shown in this drawing). The sun lay at
the very center of this Copernican universe based on geometrical spacers.