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 days the work of Tycho Brahe. They nevertheless are often referenced in almanacs and recur in Scandinavian folklore. In the Cyprianus tradition, Tycho Brahe days are considered unlucky for magical work; several of the spells in the "Black Books of Elverum" note that they should not be carried out on a Tycho Brahe day. These days were supposed to be unlucky to perform tasks such as getting married, starting a journey, or to fall ill on. Some versions claim that Tycho Brahe also identified several days as particularly lucky: Some lists omit certain days, or add others; there is no standard