Tycho and Kepler (9 page)

I
N
1945, astronomer Walter Baade made it a project to find out what the bright object was that Tycho discovered in
the sky over Herrevad in 1572. Studying Tycho’s observations, Baade concluded
¹³
that it was in all probability a Type I supernova, the explosion of a “white dwarf” star. Such a cataclysm occurs when an elderly star has exhausted all its nuclear fuel and collapsed to a sphere about the size of Earth, with a mass close to the mass of the Sun. In a star that small with a mass that huge, matter is
packed to almost inconceivable density—hundreds of tons per cubic inch. Most white dwarf stars are parts of “binary systems” in which two stars continually circle one another. The dwarf’s partner in the system is usually a much larger but far less massive star. As the two perform their celestial waltz, the denser dwarf star cannibalizes matter from its companion and gradually adds to its own mass.
The mass limit a white dwarf can attain without collapsing and exploding under the pull of its own gravity is about 1.44 times the mass of the Sun. Once having exceeded that limit, the star rips apart in a titanic explosion. That explosion is a Type I supernova.

Tycho knew nothing about supernovae. Knowledge about them was more than 350 years in the future. Tycho called the star
nova
, Latin
for “new,” though modern astronomy uses the term
nova
for a less violent explosion.

Type I supernovae happen frequently in the universe, but they are rare in any one galaxy. In our Milky Way there was one in 1006. There is no record of anyone in Europe seeing it, but in China it was called a “guest star.” Tycho’s nova was next in 1572, and in 1604 there was another, observed by Johannes Kepler.
There have been no Type I supernovae in the Galaxy since. Tycho knew of no precedent except for a report of a new star in the second century
B.C
. from the Hellenistic astronomer Hipparchus of Nicaea. Tycho ruled out the possibility that the star that heralded Christ’s birth and led the Magi was another example, on the grounds that that star had to be much nearer to Earth to lead anyone anywhere.
He was again underlining the fact that the 1572 nova did not move in relation to other stars, and hence was extremely distant, well beyond the Moon.

Radio astronomers
¹⁴
in the late twentieth century were able to identify a source of radio emission that they believe comes from what remains of the 1572 supernova. They place it exceedingly far beyond the orbit of the Moon.

fn1
Herrevad today,
still deep in the country, retains some of its medieval atmosphere, though it is now a riding school with only a small museum to recall the past. There are ancient trees, broken walls, and footings of vanished buildings, and shaded, pollen-strewn ponds that probably date from Steen Bille’s day.

4

H
AVING THE
B
EST OF
S
EVERAL
U
NIVERSES

1573–1576

SPRING, WITH THE
thawing of the sea-lanes, was the customary season for a Dane to set off on travels abroad. In spite of a new wife and the work at Herrevad, Tycho was restless again in the spring of 1573. He made plans to leave Denmark and was even thinking of making a permanent move. Details of his book’s publication delayed the
journey. He still had not left by the following autumn, when Kirsten gave birth to a baby girl, also named Kirsten, on October 10.

On November 11, Pratensis held a Martinmas feast at his lodgings in Copenhagen to mark the first anniversary of the evening when Tycho first saw the nova. One copy of the invitation still survives,
¹
promising sugar, almonds, chestnuts, a goose, a suckling pig,
and eighty bottles of wine. They were going to drink more than they were going to eat. Although Tycho may have poured scorn on the frivolities and excesses of the Danish nobility, life among scholars was not exactly abstemious.

Tycho did little observing in the summer and autumn of 1573, partly because of the distractions of publishing his manuscript. However, in early December he and his
fourteen-year-old sister
Sophie
observed an eclipse of the Moon and discovered that some adjustments he had made to the Prutenic (Copernican) Tables, while calculating when the eclipse would occur, had succeeded even better than he had hoped. “I myself cannot
²
sufficiently marvel over the fact that at this early age, only twenty-six, and without the aid of numerous and accurate observations of
the motions of the Sun and Moon, I should have been able to obtain such precise results,” wrote Tycho with unembarrassed self-approval.

Tycho and Sophie observed the eclipse from Herrevad with an elegant new quadrant
³
built to his order by specialists in Copenhagen. It was a creation of great artistic beauty, fashioned of brass and gold. Evidently Tycho’s financial situation had improved now
that he could anticipate inheriting, soon, a portion of his father’s estate.

That inheritance notwithstanding, a painting on the side of the quadrant reemphasized that Tycho had little good to say of his noble heritage. It showed a table holding symbols of aristocratic life—scepters, coats of arms, ostentatious clothing, goblets, dice. Around the table were symbols indicating the futility
of that life—a skeleton, a withered tree. On the other side of the tree the branches and roots were shown alive and abundant, and seated in its shade was a man studying a book and a celestial globe. “By Spirit we live,” declared Tycho’s inscription above the picture. “The rest belongs to death.”

The new quadrant wasn’t large or designed to make such fine measurements as Tycho’s sextant, and
it must not have been very useful, for he made few observations with it. However, Tycho clearly felt that instruments made of metals rather than wood represented the future. The quadrant was a first experiment with a relatively inexpensive model and also an exquisite trophy to celebrate his new life as an astronomer and his break with the traditions of nobility.

Figure 4.1: The brass-and-gold quadrant. The painting that repudiated Tycho’s aristocratic heritage is in the circle marked
K
and
L
. The drawing is from
Astronomiae Instauratae Mechanica
.

During the summer of 1574 Tycho moved to Copenhagen. There is no record of Kirsten and his daughter accompanying him, nor any to show whether Kirsten was “keeping the keys” of another house in accordance
with Jutish law. Knutstorp was Tycho’s widowed mother’s domain, Herrevad his Uncle Steen’s and Aunt Kirstine’s. But Kirsten was expecting their second child. The baby girl was born before the end of the year and christened Magdalene.

Tycho’s status within the Copenhagen scholarly community had been transformed with the publication of his book.
De Stella Nova
was a serious professional credential
and established him as something of an authority in astronomy. Before the summer ended, there was talk of his delivering lectures at the university, even though he had never acquired an M.A. degree or intended to have an academic career.

There had been obstacles to a nobleman publishing a book. There were even greater obstacles to his lecturing at the university. Not only his own image and
self-image were at stake but the status of others as well. Since the Reformation, church and university had become the domains of an educated middle class—usually better educated than the nobility—who served as bishops, lesser clergy, teachers, professors, and scholars. During Tycho’s lifetime and for many years thereafter no nobleman in Denmark served in these capacities. An unwritten rule of society
in sixteenth century Europe was that people, knowing their places, stayed in them and did not trespass on other territory. It was almost as unthinkable for a nobleman to move down the ladder as for a commoner to move up. It was not exactly forbidden; it just did not happen.

Someone thought of a way around this obstacle: A number of noble university students signed a petition and presented
it to the king, who then added his request to theirs, inviting Tycho to lecture to these students of his own social class. The lectures were also open to anyone else who chose to attend. After that matter was settled, it did not take long to schedule the lectures.

The first, held on September 23, was an hour-long formal introduction to the series. Two years earlier, Tycho had revealed his
philosophy and beliefs in the introduction and epilogue of his almanac. Now, in 1574, approaching age twenty-eight, he was still a religious
man
, deeply influenced by the religious traditions of his time, continuing to interpret human activity within a context of religious belief. He spoke of Seth and Moses before moving on to Hipparchus, Ptolemy, and Copernicus. As he had done in his almanac,
he argued for the value of astronomy in liberating human minds from worldly matters and turning them toward heaven, as well as for providing calendars and predicting the weather. That last usefulness had been called into question because of so many failed predictions. However, Tycho pointed out that the Sun was responsible for the seasons of the year, and many believed (though not everyone in his
time—Galileo was to be a notable exception) that the Moon influenced the tides. To Tycho it seemed reasonable to think that the stars also had to have something to do with the turbulence of weather and other weather patterns.

Discussing the use of astronomy for horoscopes was a touchier matter. Since Augustine of Hippo in the fourth and fifth centuries, nearly all Christian theologians, including
Luther, had opposed the use of astrology to predict human events. Tycho felt obliged to rebut this long tradition and to come down on the side of Luther’s disciple Melanchthon. When Tycho began this part of the lecture, nearly all in the room turned their heads to look at Niels Hemmingsen. That elderly theologian and follower (usually) of Melanchthon had recently switched his allegiance and
attacked Melanchthon’s favorable views about astrology. Hemmingsen smiled and tipped his academic hat. Then the attention reverted to Tycho.

Tycho took this hat tipping as a delightful challenge. Philippist theology (the theology of Philipp Melanchthon) had a strong hold at the university. Tycho hoped to show in what way his own views meshed with this popular thinking and how they overcame
Hemmingsen’s objections to it. The heart of Tycho’s argument was that the stars influenced individual lives and human events but did not
determine
them. He insisted that “there is something in man
⁴
that has been raised above all the stars.” God had endowed human beings with free will, and created
man
so that he can “overcome any malevolent inclinations whatsoever from the stars if he wills to
do so.” Tycho recommended good education, discipline, and other desirable human activities, for in them—in rising above a “brutish life”—lay the best possibility of deflecting the influence of the stars. Tycho would never lose his faith in astrology, interpreted as he did in this lecture, even much later when he was focusing almost exclusively on astronomy.

Tycho was a complete novice when
it came to talking before a crowd, but he must have been a riveting speaker, for after the lecture a professor of law, Albert Knoppert, approached him and commented, “When I heard
⁵
your attacks on the philosophers and physicians, and even the theologians, I was afraid that you would also launch into us jurists—so afraid that I broke into a sweat!”

The lecture crowd dispersed, but the discussion
about astrology and free will continued at a leisurely meal hosted by Dançey. Hemmingsen wanted to clarify a few points—particularly that Tycho agreed that God works and acts with absolute, unrestricted freedom and that human beings also have completely free will—and then declared himself well satisfied with Tycho’s views.

The day following this highly successful introduction, Tycho began
in earnest to lecture on astronomy. He kept no notes, and probably used none, except to record that he covered the theories of the Sun and Moon “according to the models
⁶
and parameters of Copernicus” and supplied copies of portions of the Prutenic Tables for those in the audience who could not afford to buy them.

Tycho had not, however, rejected Ptolemaic astronomy and become a convert to
Copernicanism. He explained Copernicus’s Sun-centered planetary theory, but then he proceeded to explore the possibility that Copernican theory could be interpreted in such a way as to allow Earth to stand still. In Tycho’s words, Copernican theory might be “adapted to the stability of the Earth.” A decade would have to pass before he would realize this early hope in his “Tychonic system,” but Galileo’s
nemesis was waiting in the wings.

Tycho’s attitude toward Copernicus—deep respect that fell short of acceptance of a moving Earth—would not have seemed a startling departure to the more well informed among his audience. Although Copernicus’s book
De Revolutionibus
, which had been published a month before that astronomer’s death in the spring of 1543 (about thirty years before Tycho’s lectures),
departed radically from the prevailing Ptolemaic worldview, neither the scholarly nor the religious world had reacted negatively to it. Galileo’s clash with the pope did not occur until well after Tycho’s death. Meanwhile, a great deal of time was elapsing, and no overt, dramatic conflict was occurring among scholars or theologians about how the universe was arranged.