In 1584, with the observatory of Uraniborg now too small to house all his instruments, Tycho built a second one named Stjerneborg adjacent to Uraniborg. This was the time when Tycho was most active in producing major new instruments. Thoren writes :-
Because of the number and variety of instruments made and described by Tycho, previous commentators have assumed that he made instruments for the sheer sake of keeping his instrument-makers busy. In fact, however, their construction can be traced in his logs and rationalized as several series of experiments which only produced his major instruments in the mid-1580's. The ten-year process had considerable consequences for progress of Tycho's theoretical work during his life. It has also obscured historical understanding of the accuracy of his instruments.
Maeyama notes in :-
Tycho's marvellous agreement between the description and practice of observations.
Wesley, in and , makes a careful study of the accuracy of Tycho's observations. Swerdlow, reviewing writes:-
The results of the study are interesting, and speak well for the accuracy of Tycho's instruments. Those tested are the mural quadrant, revolving wooden quadrant, revolving steel quadrant, astronomical sextant, and equatorial armillary, the last measuring declinations directly. Aside from occasional periods when one or another instrument was distinctly out of adjustment - as, by the way, only a study of this kind can show - the observations have errors falling mostly between about 0.5' and 1.0', that is, about the accuracy of the standard used for comparison. Thus, as was also the case in the earlier study of fixed stars, Kepler's belief that Tycho's observations could be trusted to better than two minutes is amply confirmed.
Among his many discoveries Tycho found that the obliquity of the ecliptic had decreased since the time of Ptolemy but, as explained in , he obtained an incorrect value due to errors by Ptolemy.
Tycho is perhaps best known today for his theory of the solar system which is based on a stationary Earth round which the Moon and Sun revolve. The other planets, according to Tycho's theory, revolve round the Sun. In fact in his younger days Tycho had been convinced by Copernicus' Sun centred model but his firm belief that theory must be supported by experimental evidence led him away. The problem was, of course, that in the Sun centred model of Copernicus a parallax shift should be observed but despite his attempts to measure such a shift, Tycho could detect none. There were two possibilities to explain this: either the Earth was fixed, or the scale of the universe was unbelievably large. We know today that it is the second of these which is true, and that the scale is such that Tycho would have had no hope in measuring parallax with his instruments. The first measurement of the parallax of a star was in 1838 by Bessel who found 0.3" for the parallax of 61 Cygni. Despite the quality of Tycho's measurements, this value in about 100 times smaller that Tycho's observational errors. In fact Tycho was not the first to propose the Earth centred model with the planets rotating round the Sun for Erasmus Reinhold had done so a few years earlier. However Rosen in argues convincingly that Tycho did not know of Reinhold's theory.
King Frederick died in April 1588 and, his son Christian (who became King Christian IV) still being a child, a regent was appointed. Support for Tycho continued however, and he presented a scheme to the Rigsraads to allow his children to inherit Uraniborg. Six of his eight children had lived. He had two sons; Tycho, born in 1581, and Georg in 1583. He also had four daughters; Kirsten born in 1573, Magdalene in 1574, Elizabeth in 1579, and Cecolie in 1582. Because Kirsten was Tycho's common law wife, their children could not inherit. Tycho, however, presented a patent which gave Uraniborg something like university status, and the director something like the status of the head of a university. It also stated that succession to the headship would give preference to "Tycho Brahe's own". Perhaps surprisingly, since the state was attempting to stop the acceptance of common law wives, Tycho's patent was accepted, a sure sign of the high esteem in which he was held (and perhaps also due to many family and friends being on the Rigsraads).
In his younger days Tycho had been a fair man in his dealings with others. Although he had treated the inhabitants of Hven badly by modern standards, and also in their eyes, it was usual for a lord at this time to treat his subjects harshly. However in the 1590s Tycho's nature seemed to change and his treatment both of the inhabitants of Hven and of his student helpers at Uraniborg became unreasonable. He always thought a lot of himself and perhaps by this stage his view of his own importance (he saw himself as the natural successor to Hipparchus and Ptolemy, a far more important person than a King) had rather turned his head. Negotiations over the marriage of his daughter Magdalene to Gellius, who had been an assistant at Uraniborg for five years, fell apart and caused Tycho extreme grief and family upset. He fell out with the young King Christian by not repairing the Chapel of the Magi at Roskilde, where Christian's father Frederick was buried, despite it being on an estate which provided Tycho with a substantial income. Christian made it clear that the promise Tycho had been given that Uraniborg would continue under the direction of his children no longer held.
Tycho closed down his observatory on Hven in 1597 (the last recorded observation is on 15 March that year), and moved to Copenhagen. However, things did not go well for him there and he left Denmark with his family and his instruments to seek support and find somewhere to continue his work :-
In 1599 he was appointed Imperial Mathematician to the Holy Roman Emperor, Rudolph II, in Prague. Johannes Kepler joined him as an assistant, to help with mathematical calculations. Tycho intended that this work should prove the truth of his cosmological model, in which the Earth (with the Moon in orbit around it) was at rest in the centre of the Universe and the Sun went round the Earth (all other planets being in orbit about the Sun and thus carried round with it).
Tycho began observing again in Prague. He received support from Rudolph for Kepler and himself to compile a new set of astronomical tables based on Tycho's recorded observations over 38 years. These would be called the Rudolphine Tables as a tribute to their sponsor. However, Tycho died eleven days after dining at the palace of Peter Vok Ursinus Rozmberk as a result of adhering to the etiquette of the day and refusing to leave the dinner table before his host. Kepler describes his death (see for example):-
Holding his urine longer than was his habit, Brahe remained seated. Although he drank a little overgenerously and experienced pressure on his bladder, he felt less concerned for his state of health than for etiquette. By the time he returned home he could not urinate any more. Finally, with the most excruciating pain, he barely passed some urine, but yet it was blocked. Uninterrupted insomnia followed; intestinal fever; and little by little delirium. ... During his last night, through the delirium in which everything was very pleasant, like a composer creating a song, Brahe these words over and over again: "Let me not seem to have lived in vain."
Field writes :-
When Tycho died, Kepler succeeded him as Imperial Mathematician. Tycho's observations of planetary positions, which were made using instruments with open sights (a telescope was not used for astronomy until about 1609), were much more accurate than any made by his predecessors. They allowed Kepler, who (unlike Tycho) was a convinced follower of Copernicus, to deduce his three laws of planetary motion (1609, 1619) and to construct astronomical tables, the Rudolphine Tables (Ulm, 1627), whose enduring accuracy did much to persuade astronomers of the correctness of the Copernican theory. However, until at least the mid-seventeenth century, Tycho's model of the planetary system was that favoured by most astronomers. It had the advantage of avoiding the problems introduced by ascribing motion to the Earth.
J J O'Connor and E F Robertson
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