Tuesday, October 28, 2008

Sidebar: Tycho Brahe

Tycho (1546-1601),despite being a Danish noble, turned to astronomy rather than politics. Granted the island of Hven in 1576 by Frederick II, he established Uraniborg, an observatory containing large, accurate instruments. His cosmology was geocentric, in opposition to Copernicus.
Tycho Brahe is probably the most famous observational astronomer of the sixteenth-century. While he is best remembered for providing the basis for the work of Johannes Kepler (1571-1630), the more colourful aspects of his life add considerable luster to his memory. Born into Denmark's high nobility, he disdained a promising career at court for astronomy. After three years at the University of Copenhagen, he spent much of the period from 1562 to 1576 in Germany, studying at the Universities of Leipzig, Wittenberg, and Rostock, and working with other scholars in Basle, Augsburg, and Kassel. At Rostock in 1566, he lost part of his nose in a duel and thereafter wore an artificial nose.
The appearance in 1572 of a "new star" (in fact a supernova) prompted Tycho's first publication in 1573. In 1574, he gave some lectures on astronomy at the University of Copenhagen. Already he was of the opinion that the world-system of Copernicus was mathematically superior to that of Ptolemy, but physically absurd. In 1576, his permanent relocation to Basle, which he considered the most suitable place for him to continue his astronomical studies, was forestalled by King Frederick II, who offered him in fief the island of Hven in the Danish Sound. With generous royal support, Tycho constructed there a domicile and observatory which he called Uraniborg, and developed a range of instruments of remarkable size and precision which he used, with the aide of numerous assistants and students, to observe comets, stars, and planets.

In 1588, Tycho published a work on a recent comet which happened to contain Tycho's system of the world. This system retained the earth as the immutable center of the universe but rendered the other planets satellites of the Sun.

In 1596 he published a volume of his correspondence with another noble-astronomer, Wilhelm IV of Hesse-Kassel, and Wilhelm's mathematician Christoph Rothmann. The latter was a committed Copernican, and Tycho's forceful arguments for the superiority of his own cosmology was one reason for his publication of the letters. Other works begun on Hven were the Astronomiae instauratae mechanica (1598), an illustrated account of his instruments and observatories, and the Astronomiae instauratae progymnasmata (1602), which contained his theory of lunar and solar motions, part of his catalogue of stars, and a more detailed analysis of the supernova of 1572. However, the erosion of Tycho's funding and standing following King Christian IV's attainment of his majority caused the astronomer to leave Denmark in 1597. In 1599 he settled near Prague, having been appointed Imperial Mathematician by Emperor Rudolph II, and was joined by Johannes Kepler the following year. He died of uraemia in 1601.

Tycho Brahe's original given name was "Tyge"; he is now known as "Tycho" the Latinized version he adopted when he was about fifteen years.

When Tycho was two years old, he went to live with his uncle and aunt, Jorgen Brahe and Inger Oxe, who had no children of their own. They acted as foster parents to Tycho until Jorgen's death. Inger Oxe was the sister of Peder Oxe who was a member of the Rigsraads, the governing council of 20 advisors to the King. In fact, Tycho's education benefited most from his foster mother, Inger Oxe, who had scholarly interests as did other members of her family, while the Brahes and the Billes had little time for scholarly pursuits.

An important administrator, Jorgen Brahe commanded several castles: Tostrup Castle, then Vordingborg Castle. In 1553, Tycho began school, most likely it was attached to a local cathedral.

On 19 April 1559. Tycho began his studies at the University of Copenhagen. There, following the wishes of his uncle, he studied law but also studied a variety of other subjects and became interested in astronomy. As a matter of fact, the accurate prediction of the actual eclipse of 21 August 1560 so impressed him that he at once began his own studies of astronomy. He purchased an ephemeris and books such as Sacrobosco's Tractatus de Sphaera, Apianus' Cosmographia seu descriptio totius orbis and Regiomontanus' De triangulis omnimodis. His foster parents decided that he should gain experience abroad and in February 1562 he set off with a travelling companion to the University of Leipzig. Astronomy was not officially part of his studies, these were classical languages and culture, but he had bought his astronomy books with him together with Dürer's constellation maps. He began making observations and by August 1563, while still at the University of Leipzig, he began to keep a record of these observations. His second observation was a conjunction of Jupiter and Saturn which proved significant for Tycho's subsequent career. Neither tables based on Copernicus nor on Ptolemy gave the correct date for the conjunction, Ptolemy's being out by nearly a month and even Copernicus' being out by days. Tycho, with typical teenage confidence, thought he could do better - and he proved to be right! Tycho now studied astronomy with Bartholomew Schultz at Leipzig who taught him some tricks to obtain more accurate observations. He knew that accurate observations required good instruments and he began to acquire them. Tycho returned home in May 1565 and in the following month his uncle Jorgen gave his life in rescuing the King. His father, who now commanded Helsingborg Castle, and mother assumed responsibility for the young man who was still under eighteen. In 1566 he was off on his travels again, visiting first the university in Wittenberg and then that in Rostock. While in Rostock he was involved in an argument with another Danish student and in the resulting duel Tycho had part of his nose cut off. A consequence of this was that Tycho developed an interest in medicine and alchemy. After his return home in April 1567 he had an artificial nose made from silver and gold. He was, however, disfigured for life and his portraits show the disfigurement which was almost certainly worse than what the artists portrayed.

Tycho's father was keen that he should quickly take up a political career but somehow Tycho persuaded his father to let him make another trip abroad. He first revisited Rostock, then went to Basel, Freiburg, and Augsburg. Tycho had been working on improved instruments for observing for a while, but when in Augsburg he designed some of his own and managed to obtain a patron to underwrite the cost of a major new instrument.

In about a month he constructed a huge quadrant and erected it in the estate of his patron outside the city. While accurate, it was so massive that it required many servants to align it for only one observation each night. Peter Ramus was in Augsburg and learned of Tycho's great quadrant; they met and engaged in deep astronomical discussions. Tycho began constructing another instrument, this time a large celestial globe made from wood.

Receiving word that his father was ill, Tycho returned home during the last few days of 1570. His father died in May 1571 and soon after, with the help of his uncle Steen Bille, Tycho began constructing an observatory in Herrevad Abbey. They also built an alchemy laboratory there since alchemy was becoming a major interest for Tycho.

In 1572 he met Kirsten Jorgensdatter, a girl from his home town of Knudstrup, but since she was a commoner and he was a noble, they could not marry legally. Kirsten lived with him, however, as his common law wife.

On 11 November 1572, he emerged into the dark of the early evening, after a long stint of alchemical experimentation, and his first glance at the sky showed him an extra star in the constellation of Cassiopeia, almost directly overhead. He instantly summoned his chemical assistant to confirm that the star really was there. He was not the first to see the new star (a supernova) but his observations of it (published in 1574) did much to prove beyond reasonable doubt that the star really belonged to the firmament and was not merely a local phenomenon in the sublunary world (as comets were generally believed to be). The star is now usually known as 'Tycho's supernova'. It turned Tycho's interest back to astronomy.

In 1574, Tycho briefly lectured on astronomy at the University of Copenhagen but stopped when he started received an annual income from his father's estate. He then set off on another trip abroad, first visiting Kassel. The Landgraf Wilhelm IV of Hessen-Kassel had founded an observatory at Kassel about 15 years earlier and Tycho was very impressed by the methods used there. Tycho's observatory was designed based on the one at Kassel, and Tycho continued ot correspond frequently with the Landgraf.

Leaving Kassel, Tycho visited Frankfurt, Basel and finally Venice before returning to Denmark at the end of 1575. With financial help from the King of Denmark, he set up Uraniborg, a famouns observatory on the island of Hven in Copenhagen Sound. This observatorywas equipped with exceptionally large and accurate instruments (it even had an alchemical laboratory in its basement). At Uraniborg, Tycho made twenty years' worth of astronomical observations.

This large facility had the main building in the center; the servants' quarters, a printing studio, and other buildings were just inside the outer walls. Tycho's design was influenced by buildings he had seen in Venice as well as a highly geometrical form.

One of the most exciting astronomical events which Tycho observed from Uraniborg was a comet on 13 November 1577. His measurements showed the comet farther from Earth than the Moon, contradicting Aristotle's model of the cosmos. Tycho's observations showed the comet further from Earth than Venus.

In 1584, he needed more room to house all his increasing inventory of large, accurate instruments; therefore, Tycho built Stjerneborg adjacent to Uraniborg. At this time, Tycho was most active in producing major new instruments.

Examples of Tycho's instruments:

  • mural quadrant
  • revolving wooden quadrant
  • revolving steel quadrant
  • astronomical sextant
  • equatorial armillary (measures declinations directly).

Accuracy from above instruments fell mostly between about 0.5' and 1.0', that is, about the accuracy of the standard used for comparison. Thus, Kepler's believed that Tycho's observations could be trusted to better than two minutes of arc.

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.

Of course, the heliocentric model of Copernicus should contain an observable parallax shift. However, Tycho could not detect such a shift despite his best efforts. There were two possibilities to explain this: either the Earth was fixed, or the scale of the universe was unbelievably large. Today we know the latter to be true; the scale of the universe 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 [26] 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 Cecilie 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 [15]:-
In 1599 he was appointed Imperial Mathematician to the Holy Roman Emperor, Rudolph II, in Prague (then the capital of the Holy Roman Empire). 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 [5]):-
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."

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.


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