Protégé of the king of Denmark Frederick II then of the Holy Roman Emperor Rudolf II in Prague.
Author of a theory of the movement of the planets, which compromised between the theses of Ptolemy and Copernicus: the Sun turns around the unmoving Earth and the other planets turn around the Sun.
1575 to 1580
Construction and organisation of the Uraniborg observatory (on the Danish island of Hveen), the largest at the time.
The observatory included a workshop which made high precision instruments- including watches indicating seconds.