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Tycho’s data

By Paolo Rossi, theoretical physicist and science historian   For many centuries astronomy has been the science which most acquired and used huge amounts of data. A good example of the extraordinary results obtained with this practice is the discovery of Kepler’s laws of planetary motion, starting from the observations performed by the Danish Tyge Ottesen Brahe (1546-1601). Of noble birth, Brahe soon showed a strong interest in astronomy. However, both for the eclipse of 1560, and for the conjunction of Jupiter and Saturn of 1563, he noticed the lack of precision in the predictions based on the data available at this time. Therefore, he devoted himself to improving them substantially, realizing the large observatory of Uraniborg. The results collected in thirty years’ time allowed him to debunk the immutability of the celestial world, by demonstrating the supernova of 1572 and the comet of 1577 must have been very far from the Earth, since their position in the celestial sphere did not change during the day and so they were external to the sublunary world, unlike what argued by astronomers and philosophers. The precision of Tycho’s observations (the Latin name used by Brahe) exceeded of an order of magnitude all the previous results, reducing the error to one arcminute, which was the best you could get with the naked eye. Against the Copernican hypothesis of a moving Earth, Tycho tried to fit the data with his own prejudice formulating a model in which the Sun rotates around the Earth, but the ...

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