Tycho Brahe, the Master Observer: A Difficult Man. Tycho's story is told all too briefly on pages 70-71 of your text. In class, I added a few embellishements to the tale of this fascinating character. For instance, I told you of his tragic death, which occurred after his bladder burst when he was unable to leave a dinner table in the presence of a nobleman; the subsequent infection led to his demise. That happened in Prague; earlier, he had lived in Uraniborg, a private observatory which was almost like a small principality in Denmark. There had his own mint, a lot of land, serfs to work the land, and so forth. Indeed, a large amount of money was spent on his endeavours by the Danish rulers, who he was later to antagonise to such an extent that he had to leave Denmark. Altogether he was a very difficult customer. In an early manifestation of his foul temper, Tycho managed to get himself into a duel in which he suffered a sword wound which cut out a piece of his nose. Apparently he was a vain man, and he had a replacement piece cast in metal (possibly even in gold) which he wore thereafter, even carrying a small box of ointment with him to keep it polished and natural looking. When his grave in Prague was opened some years ago, while a cemetary was being relocated to allow the building of a modern motorway, his skull was found indeed to bear stains on the bones consistent with prolonged contact with a piece of metal, possibly copper or some alloy, so this story is apparently true.

Two Important Discoveries.

Tycho Brahe is most important for the precision and abundance of the routine astronomical observations he made, as we will see in a moment. But he also made a couple of very important astronomical observations which had an important impact. These were the following: He discovered what is sometimes called Tycho's nova (although in modern astronomical terminology it is correctly called a supernova; we will see the distinction later in Phys 016, 'Stars and Galaxies'). This was a bright star which appeared where none had ever been seen before. (The word `nova' simply means `new' in Latin; the discovery was publicised in a manuscript describing a nova stella - a new star.) For a time it could even be seen in the daytime sky, and it remained visible for more than a year before fading away to invisibility. The importance of this was mostly philosophical: it proved that the heavens were not immutable and unchanging, which was a central part of the existing dogma. He observed a comet, and coupled his observations with those made by other astronomers some hundreds of kilometers away to deduce that the comet lay at least six times as far away as the moon , using an argument involving parallax. The true nature of comets was still mysterious, of course, but he was able to show that Aristotelian speculation about them being "atmospheric exhalations" was fruitless: they were clearly associated with the planets. And again the comet provided clear evidence that the heavens were not static and unchanging, and that things could move through the heavenly realms without necessarily being fixed in distance on some rotating crystalline sphere.

Tycho's Revolutionary Philosophy.

The two discrete observations just described had a scientific impact, but Tycho is more rightly remembered for introducing a new rigour to astronomical observing, in a couple of senses. 1 Tycho was the first scientist to recognize the importance of making lots of observations, to provide an enormous database for subsequent analysis. Night after night, he would carefully measure and tabulate the positions of the stars and planets. As we will see, this database proved essential in what was to come: some of the observations, when analyzed later by Kepler, showed that the Ptolemaic system simply failed to reproduce what was actually going on. Without excellent and trustworthy observations to show up the inconsistencies, the discrepancies might otherwise have gone unnoticed for many more decades. 2 His second contribution was just as valuable. He strove to make precise measurements, using the best equipment that he could devise. Remember that this work was done before the invention of the telescope, so he was using what were called quadrant devices, long pivoted sticks which could be moved to allow the observation of a star "in transit" -- that is, as it passed through the local meridian, moving from the eastern half of the sky to the western. Nor did he have the ability to take pictures of the sky, to get a permanent record of where a particular planet was (with respect to the stars) on a given night. He needed to keep very careful, very precise records. The instruments were beautifully calibrated to allow the precise reading of angles and so forth, and his positional data were of very high quality. It is striking to note that before the time of Tycho, not much emphasis was placed on getting data, or on its quality! Nowadays, of course, this is a central part of any serious science.

Tycho's Own 'World Model'.

Interestingly, Tycho himself was not a Copernican. He believed in a hybrid geocentric model in which the other planets revolve around the sun, but the sun itself orbits the fixed Earth. However, he did not have the mathematical skills to analyse his data and put the various models to the test. By historical good fortune, however, he hired Johannes Kepler to do that job, passing the torch to one who could do the necessary analysis. It is sad to relate that Tycho's dying wish was apparently that he "...might not be thought to have lived in vain..." -- a sentiment which is usually interpreted as meaning that he was anxious that his particular hybrid cosmological model not be overthrown. That was inevitable, though, as we will see. Previous chapter:Next chapter

0: Physics 015: The Course Notes, Fall 2004 1: Opening Remarks: Setting the Scene. 2: The Science of Astronomy: 3: The Importance of Scale: A First Conservation Law. 4: The Dominance of Gravity. 5: Looking Up: 6: The Seasons: 7: The Spin of the Earth: Another Conservation Law. 8: The Earth: Shape, Size, and State of Rotation. 9: The Moon: Shape, Size, Nature. 10: The Relative Distances and Sizes of the Sun and Moon: 11: Further Considerations: Planets and Stars. 12: The Moving Earth: 13: Stellar Parallax: The Astronomical Chicken 14: Greek Cosmology: 15: Stonehenge: 16: The Pyramids: 17: Copernicus Suggests a Heliocentric Cosmology: 18: Tycho Brahe, the Master Observer: 19: Kepler the Mystic. 20: Galileo Provides the Proof: 21: Light: Introductory Remarks. 22: Light as a Wave: 23: Light as Particles. 24: Full Spectrum of Light: 25: Interpreting the Emitted Light: 26: Kirchhoff's Laws and Stellar Spectra. 27: Understanding Kirchhoff's Laws. 28: The Doppler Effect: 29: Astronomical Telescopes: 30: The Great Observatories: 31: Making the Most of Optical Astronomy: 32: Adaptive Optics: Beating the Sky. 33: Radio Astronomy: 34: Observing at Other Wavelengths: 35: Isaac Newton's Physics: 36: Newtonian Gravity Explains It All: 37: Weight: 38: The Success of Newtonian Gravity: 39: The Ultimate Failure of Newtonian Gravity: 40: Tsunamis and Tides: 41: The Organization of the Solar System: 42: Solar System Formation: 43: The Age of the Solar System: 44: Planetary Structure: The Earth. 45: Solar System Leftovers: 46: The Vulnerability of the Earth: 47: Venus: 48: Mars: 49: The Search for Martian Life: 50: Physics 015 - Parallel Readings.

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