The emperor brings Tycho back in 1599 to Prague, where he receives financial support from several nobles in addition to the emperor, including Oldrich Desiderius Pruskowsky von Pruskow, to whom he has dedicated his famous Astronomiæ instauratæ mechanica, published in 1598.

In return for their support, Tycho's duties include preparing astrological charts and predictions for his patrons on events such as births, weather forecasting, and astrological interpretations of significant astronomical events, such as the supernova of 1572 (sometimes called Tycho's supernova) and the Great Comet of 1577.