The fact that Tycho arrived at exactly the 11' that modern theory predicts would appear to have been somewhat fortuitous, especially as he was out by about 24° in the phase of the oscillation (see Thoren (1990), Appendix 3). Details can be found in Jacobsen (1999).

Full details of Tycho's lunar latitude theories are given in Thoren (1967a).

the ecliptic. Tycho realized this and looked back at some previous observations that seemed to confirm this effect.

Ever since his patron King Frederick II had died in 1588, Tycho's status and influence had been on the decline and by the time the 19-year-old King Christian IV was crowned in 1596 he had had enough. He left Hven in April 1597, and after a few weeks in Copenhagen left Denmark altogether. He still harboured hopes that he might return to a position of power in Denmark, but when he realized that this was not to be he began to look around for another patron, and who better than the ruler of the Holy Roman Empire, Rudolph II, in Prague.

However, a problem arose in the form of his old adversary, Ursus, who since 1591 had been the Imperial Mathematician to the Emperor. Ursus found out that Tycho was planning to go to Prague and, perhaps thinking that his job was threatened, decided to counterattack. He published a book, On Astronomical

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