De stella nova... The full Latin title translates as On a New Star, Not Previously Seen within the Memory of Any Age since the Beginning of the World. An English translation can be found in Shapley and Howarth (1929).

Tycho Brahe An Oration on Mathematical Disciplines. Quoted from Moesgaard (1973).

with observation, all that was required was to re-evaluate the parameters in the Copernican models. The accuracy of his subsequent observations, however, led to the realization that this alone was not sufficient.

In 1576, in order to persuade Tycho not to emigrate from Denmark, King Frederick II granted him the fiefdom of the island of Hven for the rest of his life. Tycho liked the isolation and decided to build a great house and observatory there that he named Uraniborg, after Urania, the Greek goddess of the heavens. It took over 4 years to build and on the walls he hung portraits of Timocharis, Hipparchus, Ptolemy, al-Bitruji, Alfonso X, and Copernicus (as well as himself). Also, he had a workshop built in which a great number of ever more accurate observing instruments were produced.6

Tycho Brahe's first major contribution came in 1577 following his first sighting of a comet. He saw the comet first on 13 November and began immediately making careful observations, something he continued to do until the comet faded from view in January 1578. In November, its tail stretched 22° across the sky and the comet matched Venus for brilliance. By the end of December, Tycho concluded that the comet showed essentially no diurnal parallax and was convinced that it was further away than the Moon, at least 230 Earth radii away (about 4 times the mean Earth-Moon distance according to Copernicus). He noted that the tail of the comet always pointed away from the Sun and came to the conclusion that it was, in fact, orbiting the Sun. Once again, Mastlin was in agreement. Tycho's initial findings were written up in a report for the

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