Tycho and Kepler (17 page)

Tycho’s attitude toward his peasants and his treatment of them were not unusual. There were exceptions, of course, such as his uncle
Steen, who reportedly acted toward his tenants at Herrevad “like a mild father”
⁶
and “did not lay new burdens upon them,” which many of them “acknowledge to this day and bemoan with tears that they do miss their good master.” However, the charter of Hven served as a prototype for other similar documents all over the kingdom. It did not seem hypocritical for Tycho, in the context of the times,
to talk of Uraniborg and Hven constituting a glorious link between humankind and a love whose force drove the universe, nor did he deny that his peasants were part of that humankind. They simply had to fulfill their obligations.

Though his tenants had come to regard Tycho as a monster, and some rival scholars such as Jørgen Dybvad must have had a scarcely better opinion of him, most of Tycho’s
acquaintances during this period of his life probably found him to be an amiable, charming man. He had many of the unconscious attitudes and assumptions that went with his birth and breeding, but he was not a social snob. He had chosen a commoner for his life partner, and he preferred the company of those who belonged to a scholarly class whose social position was considered beneath his own.
However, with the completion of Uraniborg, mounting wealth, close association with the king, and particularly with the remarkable lack of opposition he was meeting as he pursued his dreams, he was undeniably developing an increasingly elitist attitude and an inflated ego that were all the more problematical because they were in many respects well founded.

With success following on success,
Tycho was beginning to equate “good” with “what contributes to the splendid work I am doing.”
Students
, assistants, and peasants should feel privileged to contribute to this magnificent venture that seemed to be favored by God and providence. There were those who did indeed see working with Tycho as likely to be their own closest brush with greatness. Tycho did not stop being an amiable, charming,
even considerate man to those who saw things in this light, whose plans supported his own lofty ambitions, or whose intellects were in sync with his. He was also subjugating
himself
to this great cause of reforming astronomy. He could not think it unreasonable to expect others to burn willingly on the same altar, be grateful for the opportunity, and be respectful of the unique responsibility that
was his.

The cause to which Tycho was dedicating himself and his great building project, and everyone around him, in the late 1570s was the achievement of a standard of observational precision undreamed of by his predecessors or contemporaries. Even the finest instrument makers had never been asked to produce instruments like those he wanted. At Herrevad he had recognized that it was essential
for him to have his own shop where craftsmen who were already skilled could become specialists and devote all their time to his needs, under his close supervision. That had not materialized there. At Uraniborg, he was making sure it did.

Tycho’s “workshop for the artisans,”
⁷
as he called his instrument shop, was admirably well equipped, beyond any other such shop in existence, with “mills
driven partly by horses and partly by water power.” Instrument building was costly in material and labor, with some instruments taking six trained people three years to manufacture while peasant labor kept the mills running.

Tycho kept meticulous records of the manufacture and use of his instruments. He had learned a lesson from the controversy about the nova: Not only did he need to achieve
instrumental accuracy to his own satisfaction, but he also had to be able to prove to others that he had achieved such precision. To that end, records had to show which instrument he used for each observation and be cross-referenced to identify
all
observations made with each instrument. For cross-checking, related observations had to be made with different instruments.

All this recording
and documenting, as well as the everyday conversation at Uraniborg in the observatories and at the dinner table, used a vocabulary of astronomy that was elementary to Tycho and his associates and students, and much of which is, in fact, utilized by modern astronomers. Ancient and medieval astronomers, and most in Tycho’s time, thought of the stars as fixed onto an invisible “celestial sphere” centered
on Earth. (That term is no longer taken literally, but the concept is still used.) The dome of sky visible at night by an observer on Earth is half the complete celestial sphere; the other half is hidden below the horizon. The stars, fixed points on the celestial sphere, serve as reference points for tracking the motion of the Sun, Moon, and planets as they move across this background.

Observing
the sky long enough reveals that the stars are not really “fixed.” Earth is turning on its axis, so the celestial sphere appears to rotate. Stars rise in the east and set in the west. Their positions in relation to one another do not change while an observer stands and watches them at night, but their positions in relation to that observer and the horizon do change.

The celestial sphere, like
Earth, has an equator—the celestial equator, which is on a plane with Earth’s equator. Also like Earth it has an axis of rotation that can be thought of as an extension of Earth’s axis of rotation. Just as Earth’s axis of rotation runs from its North Pole to its South Pole, the celestial sphere’s axis of rotation runs from the north celestial pole to the south celestial pole.

Figure 7.2: On Earth, the equator is midway between the North and South Poles. On the celestial sphere, the celestial equator is midway between the north and south celestial poles, on a plane with Earth’s equator.

The horizon is another great circle (
see figure 7.3
) that, like the celestial equator, divides the celestial sphere in half. However, while the celestial equator (like Earth’s
equator) is the same for observers in different places, the horizon is not. For Tycho, on Hven, the horizon was different from what it would have been had he set up his observatory in Basel. Stars whose paths dipped below the horizon at Hven would not have done so in Basel. Thus for any observer on Earth who is not standing on Earth’s North or South Pole, the horizon is tipped in relation to the
celestial equator. How much tipped depends on where the observer is located. The celestial equator and the horizon meet at two points, one east and one west of the observer. They are like two hoops hinged together (
see figure 7.4
).

Figure 7.3: Anywhere an observer stands on Earth’s face, except on its North or South Pole, that observer’s horizon is tipped in relation to the equator and the celestial equator. In more technical language: The observer’s horizon is inclined at an angle to the celestial equator.

Figure 7.4: Two “hoops,” the horizon and the celestial equator, are hinged together and tipped in relation to one another.

The zenith is the point directly above an observer’s head, regardless of what happens to be up there at the moment or where the observer happens to be standing on the face of Earth. Hence, as is the case with the horizon, an observer can think of the zenith as belonging
to him or her personally, while the celestial poles and the celestial equator do not—they are public property, worldwide.

There is one more hoop hinged into this arrangement (
see figure 7.5
): Tycho and most of his contemporaries believed that the Sun orbited Earth, completing one orbit in one year, moving in a great circle around Earth. (In fact, when the discussion involves only Earth and
the Sun, there is no way of deciding which is orbiting which. The two arrangements are geometrically equivalent.) Astronomy’s name for that circle was and still is the ecliptic. The ecliptic is not the same as the celestial equator, because Earth’s axis of rotation (the line drawn between the North and South Poles) does not run at a ninety-degree angle to Earth’s orbit. Like a fishing bob tilting
in relation to the surface of the water, Earth is tilted in relation to the plane of its orbit. During the summer in the northern hemisphere, the north pole tilts toward the Sun. When it is winter in the northern hemisphere, the North Pole tilts away from the Sun, while the South Pole tilts toward the Sun.

Figure 7.5: For a Ptolemaic astronomer, the ecliptic was the great circular path along which the Sun appears to travel as it orbits Earth. It is another “hoop,” with its plane tilted at an angle to the celestial equator.

The planets and the Moon also take part in the apparent daily rotation of the sky due to the rotation of Earth, but they also have additional movement of their own. To
an observer, most of the time, each of them appears to move in a great circle around Earth. These orbits are not the same as the horizon, the celestial equator,
or
the ecliptic. They are inclined at angles to these and to one another. However, the angle between the orbit of a planet and the ecliptic is never large. Pluto’s orbit is much more inclined than the others, but Tycho and his contemporaries
knew nothing of Pluto. They did know that the Moon and planets never strayed outside the zodiac, a belt of sky about ten degrees wide, centered on the ecliptic (
figure 7.6
). The position of a planet could be pinpointed by saying where it was in relation to the background stars in that zodiac belt: in other worlds, where a straight line of sight drawn from Earth through the planet would end in
the zodiac.