Tycho Brahe produce much of his astronomical data, Tycho relied heavily on the then new technique of "prosthaphaeresis", an algorithm for approximating products based on trigonometric identities that predated logarithms. Although Tycho admired Copernicus and was the first to teach his theory in Denmark, he was unable to reconcile Copernican theory with the basic laws of Aristotelian physics, that he considered to be foundational. He was also critical of the observational data that Copernicus built his theory on, which he correctly considered to have a high margin of error. Instead, Tycho proposed a "geo-heliocentric" system in which the Sun and Moon orbited
Tycho Brahe having been unable to marry the woman he loved, many of Tycho's family members disagreed, and many churchmen would continue to hold the lack of a divinely sanctioned marriage against him. Kirsten Jørgensdatter gave birth to their first daughter, Kirstine (named after Tycho's late sister) on 12October 1573. Kirstine died from the plague in 1576, and Tycho wrote a heartfelt elegy for her tombstone. In 1574, they moved to Copenhagen where their daughter Magdalene was born, later the family followed him into exile. Kirsten and Tycho lived together for almost thirty years until Tycho's death. Together, they had eight children,